What is the real reason the Spitfire 5 had single speed Merlins

Discussion in 'Engines' started by hrandy, Jul 17, 2015.

  1. hrandy

    hrandy Member

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    Most descriptions of the rushed production of the Spitfire 5 state that the two speed Merlins could not be accommodated because of their extra length. This is of course rubbish since the ever adaptable Spitfire easily accommodated the very much longer two speed two stage Merlins and even the two stage two speed Griffons with relative ease. I believe a Spitfire 5 with a two speed single stage Merlin would have been superior to the single stage engine Spitfire 5 that was quickly overwhelmed by the entry of the Focke-Wulf 190 and troubled by the Bf109F once the 109 had it's engine problems ironed out. Does anyone know the real reason why the Spitfire 5 did not get the 20 series Merlins?
     
  2. Piper106

    Piper106 Member

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    The story I have read is there was limited capacity to build two speed single stage Merlins. The Hurricane needed the two speed engine to be even somewhat competitive as a fighter, while the Spitfire was still adequate with a single speed engine (Merlin 45). So the limited number of two speed engines were used for the Hurricane II.

    Also, the two speed engine only increases performance at low allitude compared to a high allitude optimized single speed engine. If all your fighting takes palce at higher allitude, the two speed engine offers little or no advantage.
     
  3. gjs238

    gjs238 Well-Known Member

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    If the 2-speed engine helped the Hurricane so much, I wonder how a 2-speed V-1710 would have/could have helped the P-39 and P-40.
    Did the V-1650 equipped P-40F and P-40L have 2-speed superchargers?
     
  4. wuzak

    wuzak Well-Known Member

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  5. Shortround6

    Shortround6 Well-Known Member

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    It just wasn't the two speeds, the Merlin XX got the Hooker designed supercharger inlet which improves supercharger efficiency over the Merlin III, X, and XII. Please note that the Merlin 45 with the same supercharger as the XX but a single speed had a FTL of over 20,000ft in level flight. The low gear helped the Hurricane climb better at low altitudes. It also improved take-off performance, A two speed Merlin XX had about 100 more HP for take-off than a a Merlin 45.

    People are confusing several engines. The Hurricane I had a Merlin comparable to the Allison in a P-40C not the Allison in a P-40E. Getting the Merlin XX with the new supercharger and different boost and climb ratings and take-off ratings could do a lot for the Hurricane. The difference in the two Allisons was about 100hp at take-off and low altitude before WEP ratings and that is using the same supercharger gear. The later Allison was a bit better at altitude too. However without a new supercharger just providing a two speed drive was NOT going to show the improvement the Merlin XX showed over the Merlin III or X. Merlin X being pretty much a Merlin III with a two speed drive, just about all went into bombers.
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The real reason might be that Merlin 20 was in need for the bombers, plus for Hurricane, Beaufighter and Defiant. As noted, there was a limit on how many 2-speed drives can be produced for the Merlins, that British have churning out as hot rolls, outproducing the combined Jumo 211 and DB 601/605 production.
    The Merlin 20 will not turn the Spitfire into the Fw-beater just on it's own - the difference in power vs. Merlin 45 is negligible, bar the take off power. Spitfire V (or the same aircraft with Merlin 20) needs plenty of little details sorted out before it will reliably beat the 390 mph mark, and even that will not be enough in 1942 (but will even the odds a bit). The little details include a better layout of exhaust stacks, redesigned ice guard, redesigned rear view mirror, better workmanship, maybe even a fully covered undercarriage.

    Hurricane needed an engine better than Merlin III in order to came close to what Bf 109E was capable. It happened so that only such engine available in mid 1940 was the Merlin XX, indeed a 2-speed S/C engine. In the same time, the Spitifire II got the Merlin XII, an engine a bit better than Merlin III, but not as good as the Merlin 45 or the XX.

    +1 on this.
     
  7. Shortround6

    Shortround6 Well-Known Member

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    I believe part of the problem with the 2 speed Merlins was that the two speed drive was mounted inside a deeper recess/compartment in the main engine block casting (or the casting was longer). so it just wasn't a question of making more gear drive parts but changing the engine block molds at the foundry/casting facilities. I could be wrong on this.
     
  8. Reluctant Poster

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    #8 Reluctant Poster, Feb 27, 2016
    Last edited: Feb 27, 2016
    The attached illustrations indicate the length of the Merlin 45 was about half way between a Merlin III and a Merlin XX.
     

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  9. kool kitty89

    kool kitty89 Well-Known Member

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    The best argument I've seen for this (ignoring political issues within the Ministry and Hawker) was the shift in production for the Spitfire Mk.III would have delayed too much at Supermarine and focusing on the simpler Mk.V revision was the better compromise for the interim.

    Likewise, the shift in producing Hurricanes to (hypothetically) having Hawker undertake Spitfire production was also unacceptable, at least from the perspective of 1940 when critical decisions were being made. (though in hindsight, favoring Hawker-Spitfire production over Typohoon production might have been wise, particularly in terms of countering the Fw 190 threat -a clipped wing Spit III's low altitude performance should have been pretty competitive, especially as increased WEP became available)

    I'm not sure about Canadian Hurricane production, but failure to target Canadian Spitfire III production with Packard Merlins may have been another significant oversight there. (moreso as the Hurricane continued to have fire danger issues in the rear fuselage, given the continued use of fabric skin and wood stringers -though a shift to aluminum stringers and sheet should have been a better quick-fix compromise to keep the Hurricane acceptable for service)


    Continued development of Glosters F.5/34 monoplane (remember Gloster was also owned by Hawker) with Merlin XX power plant (perhaps targeting the standard/modular 'power egg' installation the M.20 used) might have been a faster/better/cheaper option than shifting to Spitfire production while offering a much more competent/modern design than the Hurricane.
     
  10. Snowygrouch

    Snowygrouch New Member

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    I suspect there are a multiude of minor contributions. However, - I`ll allow everyone here to add their own significance to it - but Supermarine WERE in progress to adapt the Spitfire airframe to the two-speed Merlin XX (as discussed, its a very obvious thing to want to do), however they were instructed part way through this work to abandon it - because the Typhoon was "due" to reach service before the convertion+retooling+production would have been completed.

    In the end due to the Sabre production problems (and some airframe issues too) the Typhoon was seriously delayed, so that put the Air Ministry in an "Oh S**T" position, where they had no Typhoon, and an even MORE delayed 2-speed SC Spitfire because they had somewhat over enthusiastically told Supermarine to not bother (there was alot of high-optimism in the Air Ministry about the hoped for performance from the Typhoon at that stage - which didnt do as well as hoped at medium-high levels, so they resorted to trying to turbocharge it).

    So the Merlin 45, was in many respects (but not all) an "oh S***T" response to having made a bad choice in telling Supermarine to stop its convertion to Merlin XX.

    I cant lay my hands right at the keyboard this moment on all the documents for this (which I do have) but here is one which tends to corroborate the non-fitment of the XX into the standard spitfire as being a problem.

    If someone really wants it I`ll try to dig out the memo on Supermarine XX work cancellation and the Typhoon being late.


    All the best
     

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  11. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Please, post your stuff :)
     
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