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Thread: Turn and Slip Indicator

  1. #1
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    Turn and Slip Indicator

    Hi All,

    Let me begin with a short Wikipedia definition :
    A standard rate turn is defined as a 3° per second turn, which completes a 360° turn in 2 minutes. This is known as a 2-minute turn, or rate one (180°/min).

    Great ! Now, let’s have a look at the British turn indicator (Turn and Slip Indicator MK1a). We can read figures on each side of the turn indicator. These are 1-2-3-4 .
    Great again ! But which one indicate a standard rate turn ?

    After several test with the Tiger Moth I think a standard rate turn can be achieved when the needle is on 3. So my guess would be that numbers represent degrees per second (and not rate of turns).

    However ...I found someone on the inernet who refered to a 1937 book« "Air Training Manual" where it’s stated "An arbitrary scale, numbered 1,2,3,4 to right and left, means that at Rate 1 a complete circle would be executed in 2 minutes, at Rate 2 in one minute, at Rate 3 in 32 seconds and at Rate 4 in 20 seconds."
    Any idea?

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  3. #2
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    Re: Turn and Slip Indicator

    Quote Originally Posted by Mix View Post
    Hi All,

    Let me begin with a short Wikipedia definition :
    A standard rate turn is defined as a 3° per second turn, which completes a 360° turn in 2 minutes. This is known as a 2-minute turn, or rate one (180°/min).

    Great ! Now, let’s have a look at the British turn indicator (Turn and Slip Indicator MK1a). We can read figures on each side of the turn indicator. These are 1-2-3-4 .
    Great again ! But which one indicate a standard rate turn ?

    After several test with the Tiger Moth I think a standard rate turn can be achieved when the needle is on 3. So my guess would be that numbers represent degrees per second (and not rate of turns).

    However ...I found someone on the inernet who refered to a 1937 book« "Air Training Manual" where it’s stated "An arbitrary scale, numbered 1,2,3,4 to right and left, means that at Rate 1 a complete circle would be executed in 2 minutes, at Rate 2 in one minute, at Rate 3 in 32 seconds and at Rate 4 in 20 seconds."
    Any idea?
    I would go with your test over a second hand quote from someone on the internet. Even in real life, instruments are not perfect and it would be a good idea to test such assumptions like you did.
    ~Uranor

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    Re: Turn and Slip Indicator

    Yes, and a reliable documentation about the real instrument would help. I haven’t find anything about it so far.

  5. #4
    Supporting Member Marco's Avatar
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    Re: Turn and Slip Indicator

    From the Air Ministry publication AP 1979A ‘Elementary Flying Training’ April 1943:


    Rate of Turn. In order to have a measure of the rate of turn which takes account of the radius of the turning circle and of our speed, we use the number of degrees of arc through which we pass in a second...The turn indicator is calibrated to show rate of turn in this way. Thus a rate-1 turn means a turn during which we cover 3 deg per second, a rate-2 turn in which we cover 6 deg per second, a rate-3 turn one in which we cover 9 deg per second.

    From AP 1275 Instrument Manual we have the following pages from the section on Turn and Slip Indicators:

    AP1275 p1.jpgAP1275 p2.jpgAP1275 p3.jpg

    Place a MkI (6A/302) next to a MkIA (6A/675 or 6A/1302) and you would be hard pressed to tell which was which, but as we can see from the last page there is a big difference in the indicated turn rates. SO...experimentation is key and even if the Mk of indicator is known it is still worth experimenting.

    Have fun.

    ~S~
    Possunt quia posse videntur (They can because they think they can) - 19 Squadron (originally Virgil)

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    Re: Turn and Slip Indicator

    That is just a great document Marco ! Thank you very much. I’ll have tests and let you know.
    BTW a quick note about the « HUD » turn indicator. It seems just inoparative.

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    Re: Turn and Slip Indicator

    So… here are the results.
    Tested on Tiger Moth at 3000 feet altitude. 65 % trottle.

    Clod Air Ministry MK1 Air Ministry MK1a
    Dial reading Rate of turn
    degrees per Minute
    Rate of turn
    degrees per Minute
    Rate of turn
    degrees per Minute
    1 75 100 170
    2 120 220 360
    3 205 360 660
    4 215 630 1080


    My tests are not perfect, they have not been done with any special measurement tools but the differences between figures are so huge that I think this instrument needs a serious calibration...
    Last edited by Mix; Jan-23-2018 at 13:15.

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  10. #7
    Supporting Member Marco's Avatar
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    Re: Turn and Slip Indicator

    The following paragraph for the
    AP 1979A ‘Elementary Flying Training’ April 1943
    quote reads:

    'We can carry out a rate-2 turn, for example, by flying along the circumference of a fairly small circle at a moderate speed, or by flying along the circumference of a larger circle at a higher speed. In both cases, we cover 6 deg per second.'

    This would suggest that whatever speed you choose to carry out the tests should be kept constant throughout the test and should be the same for all tests. Trimming should be the same and turns should be coordinated.

    Having said this I have also noticed (in Clod 4.312) there is a difference between the in cockpit Turn/Slip reading and the 'wonder woman' (no cockpit) Turn/Slip instrument reading...

    ~S~
    Possunt quia posse videntur (They can because they think they can) - 19 Squadron (originally Virgil)

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    Re: Turn and Slip Indicator

    Quote Originally Posted by Marco View Post
    This would suggest that whatever speed you choose to carry out the tests should be kept constant throughout the test and should be the same for all tests. Trimming should be the same and turns should be coordinated.
    Yes, this is what I attempted to do as the best as I can during my tests.
    Last edited by Mix; Jan-24-2018 at 02:57.

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