Vautours for the RAF ?

[Rick Lowe]

Apart from anything else, it makes it easier to come up with some flumoxing BS story to derail a JMN who's having a go at you over "accuracy" at a show. 

Our models are ALWAYS 100% accurate, absolutely identical to the thoughts that generated them in the first place! 

And we, the builders, are THE expert on that particular model anyway, by definition..............

I like that - a lot; thanks. 

[Rick Lowe]

I'm anticipating fit issues with the Spey exhausts but, I'll worry about that when it happens!

Nah, just bulge the last half-inch or so of the fuselage to accommodate the increased diameter - Done like a Done Thing!

[Weaver]

Thanks for the info   I can lengthen the fuselage, that will be quite noticeable but, increasing the fuselage depth I'd ignore. An increase in depth  of 7.5 cm per the article isn't going to be visible  in 1/48 scale (except for JMNs) so, it isn't worth bothering about (not for me anyway!   . I'm anticipating fit issues with the Spey exhausts but, I'll worry about that when it happens!

The depth amounts to about 1.5mm in 1/48th scale. In 1/72nd scale the difference in the nozzle diameters (Heller Mirage IV & Airfix FGR.2) is about 0.5mm which amounts to about 0.75mm in 1/48th. Worth remembering that the afterburner is not the engine though: within limits, designers can put any size of afterburner they like on a given engine (just look at a Draken nozzle compared to a Lightning one, both with an Avon in front of them!), so it's possible that the Spey and ATAR nozzles are pretty close. The much more non-negotiable dimensions are the engine core diameter and the intake mass flow:

ATAR: Diameter 1000mm (39 inches), Mass flow 68kg/s (maybe a bit more for the ATAR 9K in the Mirage IV: this figure is for the ATAR 9C)

Spey: Diameter 1092mm (43 inches), Mass flow 92.5kg/s

Four inches on the diameter may not seem much, but it has to come out of every fuselage frame the engine or intake passes though, times two, without making that frame any weaker than it was before. That either needs a LOT more thickness (weight inefficient) or bigger frames, which change the outside lines of the aircraft. Then there's the issue of the actual shape of the engine, where it needs access, cooling, etc...

Here's another way of looking at it: look how much IAI had to rework the back end of an ATAR-powered Mirage to turn it into a J-79-powered Kfir. Then look at how much work McDD had to do to turn a J-79-powered F-4J into a Spey-powered F-4M. Converting from an ATAR to a Spey means doing both those steps in one go.

[The Rat]

I can lengthen the fuselage, that will be quite noticeable but, increasing the fuselage depth I'd ignore. An increase in depth  of 7.5 cm per the article isn't going to be visible  in 1/48 scale (except for JMNs) so, it isn't worth bothering about (not for me anyway!

You could fudge that with a polystyrene sheet, sanded smooth at the edges. No need to cut the fuselage, just add thickness.

[Rick Lowe]

I can lengthen the fuselage, that will be quite noticeable but, increasing the fuselage depth I'd ignore. An increase in depth  of 7.5 cm per the article isn't going to be visible  in 1/48 scale (except for JMNs) so, it isn't worth bothering about (not for me anyway!

You could fudge that with a polystyrene sheet, sanded smooth at the edges. No need to cut the fuselage, just add thickness.

That'd work, and a lot less of it, too. 

[Beermonster58]

I can lengthen the fuselage, that will be quite noticeable but, increasing the fuselage depth I'd ignore. An increase in depth  of 7.5 cm per the article isn't going to be visible  in 1/48 scale (except for JMNs) so, it isn't worth bothering about (not for me anyway!

You could fudge that with a polystyrene sheet, sanded smooth at the edges. No need to cut the fuselage, just add thickness.

That'd work, and a lot less of it, too. 

Very true but, it wouldn't really be noticed and, that surely defeats the purpose? I'm not inclined to waste time and effort on something that won't be seen.      

Thanks for the info   I can lengthen the fuselage, that will be quite noticeable but, increasing the fuselage depth I'd ignore. An increase in depth  of 7.5 cm per the article isn't going to be visible  in 1/48 scale (except for JMNs) so, it isn't worth bothering about (not for me anyway!   . I'm anticipating fit issues with the Spey exhausts but, I'll worry about that when it happens!

The depth amounts to about 1.5mm in 1/48th scale. In 1/72nd scale the difference in the nozzle diameters (Heller Mirage IV & Airfix FGR.2) is about 0.5mm which amounts to about 0.75mm in 1/48th. Worth remembering that the afterburner is not the engine though: within limits, designers can put any size of afterburner they like on a given engine (just look at a Draken nozzle compared to a Lightning one, both with an Avon in front of them!), so it's possible that the Spey and ATAR nozzles are pretty close. The much more non-negotiable dimensions are the engine core diameter and the intake mass flow:

ATAR: Diameter 1000mm (39 inches), Mass flow 68kg/s (maybe a bit more for the ATAR 9K in the Mirage IV: this figure is for the ATAR 9C)

Spey: Diameter 1092mm (43 inches), Mass flow 92.5kg/s

Four inches on the diameter may not seem much, but it has to come out of every fuselage frame the engine or intake passes though, times two, without making that frame any weaker than it was before. That either needs a LOT more thickness (weight inefficient) or bigger frames, which change the outside lines of the aircraft. Then there's the issue of the actual shape of the engine, where it needs access, cooling, etc...

Here's another way of looking at it: look how much IAI had to rework the back end of an ATAR-powered Mirage to turn it into a J-79-powered Kfir. Then look at how much work McDD had to do to turn a J-79-powered F-4J into a Spey-powered F-4M. Converting from an ATAR to a Spey means doing both those steps in one go.

Yes, I understand that and, I appreciate the info . However, that is all in the REAL world.   ANYTHING goes in Whifworld!

[Weaver]

Yes, I understand that and, I appreciate the info . However, that is all in the REAL world.   ANYTHING goes in Whifworld!

Oh, of course.

On the "anything goes" principle, you could always whiffjitsu the back story to invent a scaled-down version of the Spey that was specifically designed to be interchangeable with Avons, ATARs, J-79s etc. It'd have roughly 10-15% less dry thrust than a full size Spey, but with the big Spey's afterburner, probably only about 5-10% less wet thrust. Both of those figures are still usefully greater than the ATAR, but the HUGE advantage would be fuel consumption:

ATAR-9K: 1.01 lb/(lbf·h) dry, 2.03 lb/(lbf·h) wet
Spey 202: 0.63 lb/(lbf·h) dry, 1.95 lb/(lbf·h) wet

A "mini-Spey" would probably have even better figures, especially dry.

[PR19_Kit]

On the "anything goes" principle, you could always whiffjitsu the back story to invent a scaled-down version of the Spey that was specifically designed to be interchangeable with Avons, ATARs, J-79s etc.

Rolls Royce probably did, and gave it an unintelligible 'RB' number that we'll be trying to figure out in years to come. 

[Rheged]

On the "anything goes" principle, you could always whiffjitsu the back story to invent a scaled-down version of the Spey that was specifically designed to be interchangeable with Avons, ATARs, J-79s etc.

Rolls Royce probably did, and gave it an unintelligible 'RB' number that we'll be trying to figure out in years to come. 

It was in fact the Rolls Royce  RB 165  Lossie..............not quite as big but  close to the Spey         https://en.wikipedia.org/wiki/River_Lossie

[PR19_Kit]

They you are, told you!