was the spitfire mkIX with merlin 61 cleared for 18lb boost

Discussion in 'Aviation' started by thedab, Jul 11, 2013.

  1. thedab

    thedab Member

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    and can you tell me how many with the merlin 61 as well

    thank you
     
  2. solnar

    solnar New Member

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  3. Aozora

    Aozora Well-Known Member

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    This chart from Spitfire Mk IX Performance Trials

    http://www.spitfireperformance.com/merlin-comparison.jpg

    Shows that the Merlin 61 was cleared for +15 lbs boost, while the 63, 63A, 66 and 70 were cleared for +18 lbs:

    Test of BF274 (sic) w/30 gallon drop tank:

    Spitfire F Mk IX BF274 Test

    Test of an early Merlin 61 powered Spitfire IX (BS428 bomb carrying test)

    Spitfire F Mk IX BS.428 and chart http://www.spitfireperformance.com/bs428speed.gif

     
  4. OldSkeptic

    OldSkeptic Active Member

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    And the low/mid altitude Merlin 66 (LF MK IX) was cleared for 25lb boost with 150 octane a bit later. The high altitude HF IX used the Merlin 70 which still stayed at 18lb boost, because there was no point as the supercharger couldn't deliver any more at the higher altitudes it was tasked for.

    Interesting you could get another 100-150bph at low altitude at 28lb boost for the 66 .. wonder how many operational ones were tweaked that way (a lot I suspect) since it was a field modification to go to 25lbs.
    Quick chat to the crew chief, perhaps a bit of bribery ... I'd have done it.

    http://www.spitfireperformance.com/merlin66hpchart.jpg.
     
  5. Jabberwocky

    Jabberwocky Active Member

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    #5 Jabberwocky, Jul 12, 2013
    Last edited: Jul 12, 2013
    To the best of my knowledge, the Merlin 61 was never officially cleared for anything other than +15 lbs.

    +18 lbs had to wait for the Merlin 63 onwards. Merlin 61 production was generally replaced by the Merlin 63 and 63A over the first few months of 1943. Merlin 66 production deliveries began in March or April 1943.

    There were only 730 Merlin 61 engines made, so that's the upper limit. Spitfire IX (Merlin 61) production by month for 1942 was

    June - 19
    July - 50
    Aug - 63
    Sep - 69
    Oct - 81
    Nov - 72
    Dec - 62
    Total: 416

    Production pretty much ended in March 1943, so you could probably add another 180 to 200 or so. There were also some F Mk IX with Merlin 63s delivered in November and December 1942, but no more than about 15 or 20 by the end of the year. The first LF Mk IXs with Merlin 63As were produced around the same period and delivered in early 1943.
     
  6. Shortround6

    Shortround6 Well-Known Member

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    One main difference between the Merlin 61 and the 63 (and later types) was a strengthened supercharger quill drive on the later engines. Trying to pull 18lbs boost on a Merlin 61 could overload the supercharger drive and cause a failure.
     
  7. thedab

    thedab Member

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    Good work,just what i like to see, keep it going.

    Thank, Ian
     
  8. thedab

    thedab Member

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    Right this what I saw on WWII Aircraft performance, at the bottom of the mkIX page, there is a bit on the merlin 61

    it dated from march 43, and it say that present engine rating is 15lb boost, then go on to say that the new aircraft coming

    into service with the re-rated engines operating at 18lb boost.

    Now is this re-rated engine the merlin 66?? and if it is, what is the differece between the 61 and the 66?

    Right I hope I got that right -Ian
     
  9. Shortround6

    Shortround6 Well-Known Member

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    See post #6, the Merlin 66 had the stronger supercharger drive, along with a few other changes. These superchargers needed several hundred horsepower to drive them and the more boost the more power needed. The rapid evolution of fuels sometimes meant that more boost could be used than the original supercharger drives were designed for. Breaking the supercharger drive gears or drive shaft means an earlier than expected landing ;)
     
  10. thedab

    thedab Member

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    #10 thedab, Jul 15, 2013
    Last edited: Jul 15, 2013
    that great thanks, but can the merlin 61 be upgraded to an merlin 66. i.e. like having the stronger supercharger put in and some other changes, can this be done?

    and if so was this done?

    I'm sorry about this, I'm like an 5 year old, I ask a lot of question
     
  11. wuzak

    wuzak Well-Known Member

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    #11 wuzak, Jul 15, 2013
    Last edited: Jul 15, 2013
    The 66 had a lower full throttle height than the 61. The 61 with a strengthened supercharger drive shaft was the 63. The 63 was cleared for +21psi boost on 150 grade fuel.

    Code:
    Model        61     63     66
    MS hp     1,530  1,680  1,750
    Boost       +15    +18    +18
    Alt ft   13,000  8,500  5,250
    FS hp     1,340  1,400  1,625
    Boost       +15    +18    +18
    Alt ft   23,500 15,000 12,500
    Data from Lumsden.

    Note that the extra boost on the 63 brings its full throttle height down. It woudl be safe to assume that the 63 would have the same power at +15psi boost as the 61 - since they shared the supercharger and supercharger drive ratios.
     
  12. Shortround6

    Shortround6 Well-Known Member

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    It might have been able to be done at an overhaul facility. I doubt it was done at squadron level.

    The 66 used a larger first stage impeller and different gear ratios for the supercharger, the 70 used the larger supercharger impeller and the same gear ratios as the 61 and 63.

    Some early Merlins were rebuilt to later standards but there are limits as not only are there different blocks for the one speed and two speed engines but there were changes in the block casting to beef up the later engines. You can't rebuild a Merlin III into a Merlin 61. Or later parts could be put in early engines to cut down on the number of spares needed.
     
  13. Aozora

    Aozora Well-Known Member

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    It probably could have been done, but I doubt if the conversion would have been worth it; there were a relatively small number of 61s built and these were superseded fairly quickly by the 63 series. It would have been far easier to replace the 61 with a 63 or 66 than rebuilding a 61 to 63 standards. As it was the majority of Spitfire IXs built used the Merlin 66, which was, as described, reinforced and had a low altitude supercharger which was able to be boosted to +25 lbs.
     
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