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Which variant of the Comet was the Nimrod based on?


Vulcanicity

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I've recently bought the Mach 2 Comet 4C (I know, I've opened up a world of woe and regret, but it did directly benefit the De Havilland museum and I've always wanted to do an RAF Comet.

 

Anyway said monster kit arrived today, and as I recalled someone saying that Mach 2 had erroneously based the intake depth on the Airfix Nimrod, the first thing I did when assessing the level of the task ahead was to dig the latter out to compare. (The answer (tangential to this post) is that the Mach 2 intakes are as deep as the Airfix ones and will need tedious and challenging correcting 🙈 ).

 

However the thing that really puzzled me is a massive mismatch in length. The fuselage halves of the two kits are roughly similar in overall length - but this includes the extended nose of the Nimrod and part of the extended tail boom which is moulded into the other end of the fuselage half. When you line up the fuselages at the wing roots and look at the shared Comet fuselage elements, you'll find that the Nimrod is substantially shorter in the nose to the tune of about 2.6 cm.

 

Initally, I just rolled my eyes. Great, another occasion to use the saw on this kit - Mach 2 have got it way too long. The Nimrod is based on the Comet 4C, right? The basic fuselage should be the same length, plus the add-ons at each end.

 

However, the 2.6 cm difference in "actual" fuselage length scales quite well to the 2 m, 2-window fuselage stretch between the BOAC-standard Comet 4C and the later, lengthened 4B/4C fuselage. And the Mach 2 scales remarkably well to the 35.99 m length of the 4C. The Airfix Nimrod, at least, seems to be based on the Comet 4 length and not the 4C.

 

So my question is: was the real Nimrod actually based on the Comet 4 fuselage and not (as I've always assumed) the more up-to-date 4C? If so, then why? By the mid 60s the "stretched" Comet design had been successfully flying around for several years, and 2m more fuselage would presumably have been useful space for payload, avionics, fuel, or all three.

 

To add to this, every mention I can find of Nimrod prototypes XV147 and XV148 says that they were the last two Comet 4Cs off the production line which were modified before completion to partial Nimrod standard. However the  pictures I can find of XV147 (which had more or less the full complement of Comet windows) show only six windows forward to the over-wing gap in the window line (per Comet 4) rather than eight (per Comet 4C).  So what's going on?
 

  • Is the Airfix Nimrod kit about 2 cm too short? If so, I have never seen any reference to this.
  • Were XV148 and XV147 actually short fuselage Comet 4s? What were they still doing on the production line in the mid 60s, if so?
  • Were 147 and 148 modified during to conversion to Nimrod status to revert them to the shorter length? (with production Nimrods following) If so, why?
  • Have I missed something else?
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I was trying to remember from my Nimrod 'Q' course in Mar 82 in which the instructor mentioned something about the Nimrod being shorter than the Comet from which it was converted and how the AEW Mk3 could do with this now for the computers that BAe wanted to put in, but you know how the memory plays tricks on you. Anyhow I have found in the Ian Allan Modern Combat Aircraft No 24 about the Nimrod which says "from the start Nimrods were in fact 6ft shorter from nose to rudder than the Comet 4Cs, a plug being taken out of the fuselage immediately ahead of the wing with a view to this improving the directional stability, and it was thought that the ECM aerial fairing on top of the fin might help too. In the event the pannier, especially with its doors open, had added enormously to the total keel area and the loss of those 6ft was later regretted".

 

In the book it does say that XV148 and 7 were Comet 4Cs, but does not say if the above conversion was carried out. Personally I do not think that it was and they were straight aerodynamic conversions. XV148 was an unfinished airframe and had Speys fitted whilst XV147 was a completed build and retained its Avon 525B engines.

 

I hope that this is of some help.

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Curious. The AEW prototype was a 4C (ex BOAC) and doing the Avionic fit for both the Comet and the Nimrod, I don't remember the difference in length. Laying out the Nimrod fuselage we used Hawker Siddeley's Comet drawings - but of course they could have been Comet 4 drawings! The Nimrod definitely looks shorter than the 4C. I do remember the +/-6 inch tolerance on overall length 😮

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The Nimrod design was based on the Comet 4, length 111'6", span 114'10".

The prototypes (XV147 & 148) were converted from two available Comet 4Cs that were spare airframes at the time, these being shortened to Comet 4 length.  XV148 also retained the original Avon engines.

 

Comet 4 G-APDS became XW626 and converted to an AEW trials machine as part of the Nimrod AEW trials programme. It was essentially the same length as a Nimrod.

 

 

 

Edited by 71chally
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20 hours ago, Vulcanicity said:

I've recently bought the Mach 2 Comet 4C (I know, I've opened up a world of woe and regret, but it did directly benefit the De Havilland museum and I've always wanted to do an RAF Comet.

 

Anyway said monster kit arrived today, and as I recalled someone saying that Mach 2 had erroneously based the intake depth on the Airfix Nimrod, the first thing I did when assessing the level of the task ahead was to dig the latter out to compare. (The answer (tangential to this post) is that the Mach 2 intakes are as deep as the Airfix ones and will need tedious and challenging correcting 🙈 ).

 

Are you documenting your build on here?  If so, I'd be very interested to see more in detail of the Mach 2 kit, especially photos of the contents and also what it is like to build & correct.  Whilst I am aware of its reputation, and have seen a couple of pics showing completed ones, I'd much prefer to work with styrene than with resin & vac form.

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4 hours ago, 71chally said:

 

The prototypes (XV147 & 148) were converted from two available Comet 4Cs that were spare airframes at the time, these being shortened to Comet 4 length.  XV148 also retained the original Avon engines.

 

According to all info that I have and as I mentioned in my earlier post it was the other way around with XV147 keeping the Avon engine and XV148 as it had not been fully built in the first place getting the Spey engines.

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That's really interesting, thanks all! HS must have been seriously worried about stability to go to the lengths of cobbling the aircraft back to the previous length. I wonder if there might also have been a concern about structural strength, with all the increased weight of the Nimrod being too much for the "stretched" fuselage?

20 hours ago, Paul H said:

 

Are you documenting your build on here?  If so, I'd be very interested to see more in detail of the Mach 2 kit, especially photos of the contents and also what it is like to build & correct.  Whilst I am aware of its reputation, and have seen a couple of pics showing completed ones, I'd much prefer to work with styrene than with resin & vac form.

 

Hi Paul - I probably will do but not soon, as I've got a lot of builds higher up the pile. From a quick look the big things to correct are:

  • Window line - the oval kit window apertures  are not only not in a straight line (minor issue), but also tilted more or less at random away from the horizontal (major issue).  My current thinking involves cutting the whole window panel out of each fuselage half, discarding it and preparing a new section from a length of plumbing waste pipe, possibly using the Nimrod as a drilling template for a short row of windows, repeated and spaced appropriately to recreate the whole line.
  • Nacelles. As I understand the Nimrod retained the contours of the upper wing root  but the underside was deepened to accommodate the Speys. So I think this will be a case of cutting a section out of the bottom, cutting some depth out of this then re-fixing and making good with filler.
  • Exhausts: Far too small and very clumsily moulded. I will be getting the Whirlybirds set. New engine faces are also needed, somewhere I have some Avons I cast in Fimo clay from the Airfix Valiant years back.

Other than that it's just a case of rough moulding, overly thick parts and rather clunky detail. I'll try and do a brief inbox review at the weekend on the Rumourmonger thread with some photos

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There's a picture of XV148 on the production floor (I think in the Haynes Comet manual) where you can see the line on the fuselage where it was cut'n'shut to reduce the fuselage length

Couple of nice pics of XV147 here showing the smaller intakes (albeit behind blanks)

https://www.skippyscage.com/aviation/uk/farnborough/198306.php

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For the concept and for much of the Nimrods' career there wasn't seen the use for the longer fuselage.  The original MR.1 was quite austere compared with the MR.2, and the later version housed the equipment and rest stations etc without too much of a problem.  Basing it on the 4C would have introduced more weight, and I wonder if more unwanted flex, given that so much of the ops was bouncing around at low-level over the sea.

In reality it wasn't 'cobbled' to a shorter length, it would just have been built on the Comet 4 jigs and components.

 

Where I have heard any criticism of the design was that the Comets' fuselage was felt to be narrow.  The P-3 (incidentally shortened compared to the Electra that it was based on) seems more spacious inside, but that might be down to the layout.

I knew someone who worked on the Nimrod AEW radar programme, and he mentioned that the fuselage was felt to have been too cramped for that role.

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16 minutes ago, Dave Fleming said:

Couple of nice pics of XV147 here showing the smaller intakes (albeit behind blanks)
https://www.skippyscage.com/aviation/uk/farnborough/198306.php

Great angle, as it also shows well the unique generators housings under the Avon engines, needed for the electrical demand of the Nimrod.

 

You can also the tell the fuselage is shortened as it has the same amount of windows as a Comet 4, rather than the 4C that it was constructed as.

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4 hours ago, Vulcanicity said:

That's really interesting, thanks all! HS must have been seriously worried about stability to go to the lengths of cobbling the aircraft back to the previous length. I wonder if there might also have been a concern about structural strength, with all the increased weight of the Nimrod being too much for the "stretched" fuselage?

 

Hi Paul - I probably will do but not soon, as I've got a lot of builds higher up the pile. From a quick look the big things to correct are:

  • Window line - the oval kit window apertures  are not only not in a straight line (minor issue), but also tilted more or less at random away from the horizontal (major issue).  My current thinking involves cutting the whole window panel out of each fuselage half, discarding it and preparing a new section from a length of plumbing waste pipe, possibly using the Nimrod as a drilling template for a short row of windows, repeated and spaced appropriately to recreate the whole line.
  • Nacelles. As I understand the Nimrod retained the contours of the upper wing root  but the underside was deepened to accommodate the Speys. So I think this will be a case of cutting a section out of the bottom, cutting some depth out of this then re-fixing and making good with filler.
  • Exhausts: Far too small and very clumsily moulded. I will be getting the Whirlybirds set. New engine faces are also needed, somewhere I have some Avons I cast in Fimo clay from the Airfix Valiant years back.

Other than that it's just a case of rough moulding, overly thick parts and rather clunky detail. I'll try and do a brief inbox review at the weekend on the Rumourmonger thread with some photos

I'd be interested in seeing how you get on with this project.  One of the many visible errors in the Mach 2 kit appears to be a pronounced kink in the outboard portion of the wing, and resulting dihedral change, that I do not see in any photos of the real thing.  This is not impossible to correct, of course, but it is an annoyance.  If only A-Model would do a Comet 4 series in 1/72--I think they'd get it right.

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3 hours ago, TheyJammedKenny! said:

I'd be interested in seeing how you get on with this project.  One of the many visible errors in the Mach 2 kit appears to be a pronounced kink in the outboard portion of the wing, and resulting dihedral change, that I do not see in any photos of the real thing.  This is not impossible to correct, of course, but it is an annoyance.  If only A-Model would do a Comet 4 series in 1/72--I think they'd get it right.

Oh God not more things to fix! I had noticed the dihedral but it hadn't really registered as a potential issue. Oh well, it can be cut and shimmed I suppose..

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