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  1. #1
    F-UK FLYER
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    Confused by an RPM Gauge on a 914 POWERED Microlight.

    Confused by an RPM Gauge on a 914 POWERED Microlight.

    Today (23/01/2018) I flew in a Rotax 914 powered Microlight that had a confusing set of engine dials
    The microlight had a CS Propeller so it has a MAP Gauge & it also has a RPM Gauge, now being a Rotax 914 it has turbocharging so it will show 39 - 41in MAP on take off. I must admit I expected to see 5800rpm on the RPM on Take off but I noticed it only hit what looked like 2400rpm !!!
    ( I was the passenger for the take off so I wasn't 'checklisting'....... I was going to be P1 for the sectors after this sortie so I didn't pay attention too much to this departure ).

    I probably didn't get startled by the 2400rpm because I am used to GA engines running at that figure & this microlight had taken off like a scolded cat so I knew it felt like it had produced FULL POWER.

    The weird bit was in the cruise the engine was set to 2000rpm 31in MAP.

    I spent ages trying to get my head around these figures on a Rotax 9 series engine ( even though they made sense if I was flying a GA aircraft ).

    Now comes the answer : There is a company that now make a Rev Counter for Rotax 9 Series engines that shows the Prop RPM as opposed to the Engine RPM ( It is a great idea for us Dye in the Wool GA Jockey's who dabble in microlight aircraft ) though I am sure it would serve perfectly well for microlighters as well to get these Rev Counters as well?

    So for simplicity 2380rpm shown on the Rev Counter equals 5800rpm engine speed.....2250rpm equals 5500rpm engine speed.....2000rpm equals 5000rpm engine speed.

    What do you guys think about having a Rev Counter that shows Prop RPM instead of Engine RPM?
    I know seeing Engine RPM is the Rotax norm but I can see a lot of sense in having a Rev Counter that actually shows figures that relate to what you usually see in GA Aircraft.
    ( I find relating 2000rpm 31in MAP for a turbo'ed Rotax easier to understand than 4860rpm 31in MAP )

    Is this a move to getting something else nearer to GA standards seeing as the gap between microlights & GA aircraft is getting ever smaller?


  2. #2
    Captain Randombloke's Avatar
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    Quote Originally Posted by F-UK FLYER View Post

    Is this a move to getting something else nearer to GA standards seeing as the gap between microlights & GA aircraft is getting ever smaller?
    Could be, tell us what the aircraft is and we can have a look at the POH and see for ourselves...
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"


  3. #3
    F-UK FLYER
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    Quote Originally Posted by Randombloke View Post
    Could be, tell us what the aircraft is and we can have a look at the POH and see for ourselves...
    Blackshape Prime.

    The link to the gauge fitted is attached below. The gauge can be fitted into anything that has a 912S or 914 fitted.
    They do one for the 80hp 912 as well
    Attached Files Attached Files


  4. #4
    Co-Pilot paultheparaglider's Avatar
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    Most GA aircraft do not have an engine reduction system such as a gearbox or a belt and pulley system. So engine rpm equals prop rpm. Your average engine and hence prop rpm in your typical lycosarus are in the region of 2200 to 2600.

    By one of those lucky coincidences in life, manifold pressure, which is usually measured in GA aircraft as inches of mercury runs in a fairly similar range of absolute numbers.

    Flying at 2400 rpm and 24 inches is called flying square, and it used to be considered unwise to fly oversquare where the manifold pressure exceeded the rpm (/100). This isn't always true, but the general rule is throttle down before prop down, and prop up before throttle up with a constant speed prop. Clearly, having a rpm gauge that measures prop rpm rather than engine rpm for a geared engine takes away the mental calculation that would be needed otherwise to avoid oversquare. This is a very much debated issue in the GA world, and many do advocate flying oversquare when cruising.

    https://www.avweb.com/news/airman/184483-1.html


    Now, Peter (F-UK) knows this because he will probably have a CSU (constant speed unit) differences rating in his logbook, as do I, and he is simply once again trying to display the superiority of GA pilots over we microlight plebes as we normally use fixed pitch props.

  5. The Following 2 Users Say Thank You to paultheparaglider For This Useful Post:

    Randombloke (24-01-18), renmure (24-01-18)


  6. #5
    F-UK FLYER
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    Quote Originally Posted by paultheparaglider View Post

    Now, Peter (F-UK) knows this because he will probably have a CSU (constant speed unit) differences rating in his logbook, as do I, and he is simply once again trying to display the superiority of GA pilots over we microlight plebes as we normally use fixed pitch props.
    Paul, Much as you might feel this is a cunning plan to try to exude supremacy over microlighters it isn't.
    Yes I do have ratings on this for GA stuff, I was genuinely surprised to see a Prop RPM Gauge in something that I naturally expected to have the gauge I am now primed to see in a microlight panel that measures Engine RPM.

    So, the reality is : This GA Pleb found it initally strange but then for all the reasons you mention above I found it less taxing on my few braincells to square things up
    914 is actually turbocharged so it is 'oversquare' all through the range.


  7. #6
    Captain woodysr2's Avatar
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    Strange I didn't think there were any on the UK register must go and look up g info.
    fly high fly safe and may you always have the wind at your back
    (except when taking off or landing according to Phil )


  8. #7
    F-UK FLYER
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    Quote Originally Posted by woodysr2 View Post
    Strange I didn't think there were any on the UK register must go and look up g info.
    William,
    The Playground is a bit bigger than England, Wales, Ireland & Scotland....... there is a lot more out there to play in.
    Who mentioned a UK registered Blackshape?
    europe-map-editable.jpg


  9. #8
    Captain woodysr2's Avatar
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    Funnily enough I know what a map looks like and have actually been and flown on more than one continent in a variety of aircraft from hangliders to helicopters.
    I was just surprised that you were in a black shape as I had not heard that any of our European flying buddies were over visiting and word normally gets round of visiting aircraft especially if a tad unusual
    It would have been nice to see in the flesh (the plane that is)


  10. #9
    F-UK FLYER
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    Quote Originally Posted by woodysr2 View Post
    I was just surprised that you were in a black shape as I had not heard that any of our European flying buddies were over visiting and word normally gets round of visiting aircraft especially if a tad unusual
    It would have been nice to see in the flesh (the plane that is)
    Why would you be surprised? I tend to keep myself to myself nowadays and my European flying buddies tend to leave UK visitation arrangements to me to organise, I am not into the 'open publicity' of what is happening in my aviation circles since there are some snidey tykes around. However if a Blackshape crosses Hadrians Wall I will ensure that you get an opportunity to see it in the flesh ( the plane that is ).


  11. #10
    Captain Roger Mole's Avatar
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    William, here's a shot I found on the internet of an intrepid French pilot practising his manoeuvres before bravely embarking on his cross-Channel flight to infinity and beyond.

    If I'm not mistaken, he's in a Blackshape, all over-square with constant speed everything, so it'll be well worth looking out for if he does make the trip.

    1984ja10.jpg

    Apparently his European flying buddies are all up for him to make the trip and can't wait for it. I'd keep my eyes open on Faceplant and Imajury if I were you.
    Last edited by Roger Mole; 25-01-18 at 21:30 PM.


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