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View Full Version : WOuld using the Merlin XX on the SPitfire V have led to a better aircraft?



Xiolablu3
09-01-2008, 07:07 AM
HI guys, this is soemthing I have always wondered, seeing quotes such as 'the Merlin XX was reserved for the Hurricane as it was felt that it needed the upgrade more than the Spitfire'

Did the Merlin 45 really supercede the Merlin XX, or would the Merlin XX have made the Spitfire V a better performer?

From what I can see, the Merlin XX was as powerful as the Merlin 45 but had a two speed , two stage supercharger, wheras the Merlin 45 had a single stage, meaning it was much worse at high altitudes.

From the figures I have, the Melrin XX is only a little less powerful than the later Merlin 61 (1480hp vs 1580hp), both with dual stage dual speed superchargers.

However I dont know enough about this to make an informed decision and am hoping for insight.

Thanks for your comments.

Xiolablu3
09-01-2008, 07:07 AM
HI guys, this is soemthing I have always wondered, seeing quotes such as 'the Merlin XX was reserved for the Hurricane as it was felt that it needed the upgrade more than the Spitfire'

Did the Merlin 45 really supercede the Merlin XX, or would the Merlin XX have made the Spitfire V a better performer?

From what I can see, the Merlin XX was as powerful as the Merlin 45 but had a two speed , two stage supercharger, wheras the Merlin 45 had a single stage, meaning it was much worse at high altitudes.

From the figures I have, the Melrin XX is only a little less powerful than the later Merlin 61 (1480hp vs 1580hp), both with dual stage dual speed superchargers.

However I dont know enough about this to make an informed decision and am hoping for insight.

Thanks for your comments.

No41Sqn_Banks
09-01-2008, 07:38 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Xiolablu3:
From what I can see, the Merlin XX was as powerful as the Merlin 45 but had a two speed , two stage supercharger, wheras the Merlin 45 had a single stage, meaning it was much worse at high altitudes.
</div></BLOCKQUOTE>

The Merlin 45 had only single stage but this stage was optimised for high altitude. The Merlin 45 had bad low altitudes and good high altitudes performance. Therefore a Spitfire V with a Merlin XX would have been good in low and high altitudes. By the way the Spitfire III was the Spitfire mark with the Merlin XX.

OMK_Hand
09-01-2008, 07:54 AM
Hi Xiolablu3,

Here's a potted history taken from 'Spitfire Mark V In Action', by Peter Cayhill.

"The first attempt to increase the performance of the basic spitfire design resulted in the Mk.III, which first flew on the 16th March 1940...

... It was powered by a 2 speed supercharged Merlin XX of 1,390hp, the use of which required strengthening of the forward fuselage and engine mountings. Other modifications included a general beefing up of the undercarriage legs, which were also angled forward by a further 2 inches in an attempt to avoid the Spitfire's tendency to nose over in soft field conditions. Many other changes also...

... Almost from the word go, however, the Spitfire III was in trouble. Development difficulties with the Merlin XX led to delays, and the decision was taken to award engine priority to the Hurricane II, which would have quickly become obsolescent without it...

... But the main danger to the Mk. III came from the Luftwaffe...

... New Me109F, new Ju 86P reconnaissance... Greatly worried Air Ministry and led to belief that new offensive would be fought at greater heights than BoB.

The main production difficulty with the Merlin XX concerned its low-altitude blower, but ironically the new RAF operational requirement was heavily weighted towards performance at higher altitudes...

In parallel with the Merlin XX, Rolls Royce had been developing a similar version, which featured a single blower of 10.25 diameter.
Known as the Merlin 45, it gave a power output of 1,440hp and promised to make the spitfire much more effective at greater heights...
Also easily adapted with minimum modification to Mk I/II airframe.

Result; Spitfire III killed off, Mark V approved on 6th March 1941 as a temporary expedient', a short term solution to the immediate problem of high altitude attack."

Kurfurst__
09-01-2008, 07:55 AM
Merlin 45 = Merlin XX 'light'.

AFAIK the whole idea behind the 45 was to provide an easily available Merlin with better high altitude performance compared to the more complex Merlin XX. So they simplified the Merlin XX.. The Mk V itself was the sort of improvized interim solution that could be readily produced quickly to fill in the ranks, until the more advanced types become available.

And it turns out that these so-called 'interim solutions' in wartime become the most important types, the ones that do most of the fighting...

So as to the original question, would the Merlin XX powered Spit V have been a better aircraft? Most likely the answer is yes. At the same time, it would have been much less available when it was most needed.

Xiolablu3
09-01-2008, 08:07 AM
Thanks for your input guys, very interesting, sorry I got it the wrong way around, the MkVB was optimised for high alt, not low alt.

Thanks for the correction.

WTE_Galway
09-01-2008, 08:34 PM
Also bear in mind that by late '41 the Tiffies were about reducing the need for Spit's to go scud running at low altitudes.

Viper2005_
09-01-2008, 10:14 PM
The Merlin XX had a single stage, two speed supercharger.

The Merlin 45 had a single stage, single speed supercharger.

They shared the same supercharger, which thanks to ****** was considerably more efficient than that featured in the first generation Merlins.

The Merlin 45 could be produced on existing tooling, whereas the Merlin XX required new tooling due to the two speed supercharger gearing.

Merlin XX production was limited due to the lack of tooling. The Hurricane II ended up with the Merlin XX because without it it would have been unable to compete; retooling for an alternative aeroplane would have incurred an even greater cost.

Obviously a Spitfire V airframe with a Merlin XX engine would have exhibited superior performance at low level; the 45 is just a XX without its low gear.

But in the context of WWII it was adjudged that the best use of the Merlin XX was keeping the Hurricane II viable rather than polishing the Spitfire.

Bela2008
09-01-2008, 11:11 PM
A further question:

I believe the Merlin powering the early Spit V was subject to carburettor flooding in even short bursts of inverted flight (same with Hurricane).
Can anyone confirm this?

the DB600's of the Bf109 family had fuel injection and could pull out of a dive much more easily than Spits and Hurricanes.

Without fuel injection such as in the DB600's of the BF109 how would installing a MerlinXX overcome that disadvantage?... or did it too have fuel injection? Or how was the carburettor problem overcome in the Merlin?

Viper2005_
09-01-2008, 11:28 PM
http://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice

Xiolablu3
09-01-2008, 11:30 PM
Its not the pulling out of a dive that was the problem, its the entering of a dive if you pushed forward on the stick, when the engine would splutter and the very early Merlins you would lose vital seconds.

Howeve, just as the Spitfire V was coming off the production lines in March 1941, Miss Shilling was travelling around the Squadrons putting in her 'orifice'. So the SPitfire V's had possibly a very short period where they had the fuel starvation problem, and it was proabably only weeks or even days for the front line squadrons, which she would obviously fit first.

Bela2008
09-01-2008, 11:50 PM
Thanks,

All is explained now in the Battle of Britain movie (Michael Caine, Christopher Plummer etc.) where in the opening scene a Hurricane does a roll and coughs - or backfires - at the moment of inversion (stick forward to keep the nose level in inversion).

ImpStarDuece
09-02-2008, 12:34 AM
In hindsight, a better solution could of been to scrap the Defiant Mk II, which had a Merlin XX, and was operational by February 1941.

This way, the 220-odd Merlin XX engines set aside for Defiant production could of been allocated to Spitfires. That is enough for about 10 squadrons worth of fighters.

I can't remember which factory ended up with the Spitfire III order though. This might of had a real bearing on whether a Merlin XX engined variant could of been produced alongside the Merlin 45 engined variant.

I have a graph of Merlin XX performance vs Merlin 45 performance kicking about somewhere. From what I can recall, the XX engined variant was about 5-15 mph faster at low to medium altitudes, but a few miles slower at high altitudes, and speed dropped off at altitude faster than the Merlin 45. Will have to dig it up.

WTE_Galway
09-02-2008, 01:30 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Xiolablu3:
Howeve, just as the Spitfire V was coming off the production lines in March 1941, Miss Shilling was travelling around the Squadrons putting in her 'orifice'. So the SPitfire V's had possibly a very short period where they had the fuel starvation problem, and it was proabably only weeks or even days for the front line squadrons, which she would obviously fit first. </div></BLOCKQUOTE>

Bela 2008 is correct on this one .. the early Merlins got to much fuel and flooded under negative G. It was not fuel starvation.

The famous "orifice" was actually just a restrictor to limit how much fuel could get into the float chamber preventing the flooding.

Xiolablu3
09-02-2008, 01:32 AM
SOrry, yes of course.

WTE_Galway
09-02-2008, 01:38 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Xiolablu3:
SOrry, yes of course. </div></BLOCKQUOTE>

It can make a difference as a flooded engine can spontaneously restart at inopportune times if not immediately feathered and throttled back http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

This is almost certainly the reason for the fatal Mosquito crash in England during the 1990's. Incorrect engine maintenance meant one engine flooded under negative G at an airshow. The evidence shows they throttled back the good engine and regained control only to have the dead one restart at full throttle.

luftluuver
09-02-2008, 04:52 AM
The negative g was a two stage event. At the onset of negative g, fuel was forced to the top of the float chamber, which exposed the main jets to air. This caused the first momentary, lean cut-out. If the negative g condition continued, the float reacted to the reverse of normal conditions and floated the wrong way, that is, they floated to the bottom of the float chamber. The needle valve opened wide, allowing full fuel pressure from the the engine driven pump to flood the carburetor. An excessively rich mixture was then admitted into the supercharger causing the more serious rich cut-out.

There was 2 orifices, one for 12lb boost and another for 16lb boost.

from White's book on WW2 engines

The definative fix was the single point fuel injection of the Bendix or later R-R type.