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  • Re: Think I need my prop repitched. Any suggestions?

    by » 8 months ago


    Static rpm is different for 2 blade vs 3 blade and different props. So static only gets you in the ballpark and you need to fly each plane to fine tune the pitch. Plus you may have a need for a better climb prop vs balancing  out your climb and cruise pitch. 

    You must differentiate between fixed pitch / ground adjustable vs in flight adjustable. Many regions or Mfg's don't  use or allow in flight adjustable that would be best. So if you have a ground adjustable then other factors should be considered.

    A prop can be over or under pitched. It has a pitch range to make it efficient and effective. Anything rpm under 5500 at WOT in level flight is over pitched and any pitch that allows anything over 5800 WOT in level flight is under pitched. In either scenario you lose performance. A pitch that yields less than 5500 WOT in level flight cost you everything. More fuel, higher engine and oil temps, loss of climb and cruise. There are NO redeeming qualities  in an over pitched prop. Anything under that 5500 WOT in level flight stresses the engine and you lose climb, cruise, fuel economy  and have higher oil temps on climb out. In the older crank cases over pitching could cause a crack in the case.

    So the Rotax spec of 5200 at take off usually gets you around the 5800 WOT mark in level flight. ( different aircraft designs can play a part here) So if you get 5800 WOT then you're  on the better climb pitch side. Reduce that to 5600 - 5650 WOT in cruise which is only 150 - 200 rpm lower and is about 5000 - 5100 rpm on take off will give you a good balance between climb, cruise, fuel economy and engine temps. Thousands of owners do this without any issues.

    If you have a heavy plane, an amphib or a need for a better climb prop like a short field then 5800 is a good target. If you have no real need for a better climb pitch then 5600 - 5650 will balance out your performance. 

    As far as higher oil temps there are other things  that cause this and it's not just prop pitch. 


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Think I need my prop repitched. Any suggestions?

    by » 8 months ago


    912isPower,

    I don’t know the RPM change per degree for your prop, Roger probably does. I think you will get something like 200 RPM/degree, so I would start with 1 degree at a time until you get around 5000 RPM static, then fine tune by 1/2 degrees.  There was a service bulletin recommending a takeoff RPM of 5200 or more but I don’t believe that applied to the iS engine, and I think it was targeted at adjustable prop aircraft.  

    After each adjustment do a ground run-up to check the static RPM WOT. When you get 5000-5100RPM go fly and check the max RPM during climb and WOT level flight at your average altitude. You can check your performance and engine temps and decide if you want to make further adjustments.  You have to fuss with it a bit, but the results will be worth it. You can think of the prop pitch like the gears on a bicycle, and right now you are trying to pedal uphill in high gear.  Unfortunately with a fixed propeller you have to choose one gear for the entire ride.  

    As far as exhaust gas temperature, it has been my experience that you can expect higher EGTs (especially in ECO mode which is lean of peak) as you move to a lower pitch with the iS engine.  This won’t be a problem, the operating manual allows for EGT up to 1742 deg f., and I never saw temps over 1650 at any prop setting. Conversely, you will likely see lower CHT and oil temps as you move to a lower pitch on the prop and unload the engine.  The combustion heat goes somewhere… the more you load the engine the more of that heat goes into the cylinder heads, and as you unload the engine more goes out the exhaust. 


    Thank you said by: Jonathan

  • Re: Think I need my prop repitched. Any suggestions?

    by » 8 months ago


    Roger Lee wrote:

    Static rpm is different for 2 blade vs 3 blade and different props. So static only gets you in the ballpark and you need to fly each plane to fine tune the pitch. Plus you may have a need for a better climb prop vs balancing  out your climb and cruise pitch. 

    You must differentiate between fixed pitch / ground adjustable vs in flight adjustable. Many regions or Mfg's don't  use or allow in flight adjustable that would be best. So if you have a ground adjustable then other factors should be considered.

    A prop can be over or under pitched. It has a pitch range to make it efficient and effective. Anything rpm under 5500 at WOT in level flight is over pitched and any pitch that allows anything over 5800 WOT in level flight is under pitched. In either scenario you lose performance. A pitch that yields less than 5500 WOT in level flight cost you everything. More fuel, higher engine and oil temps, loss of climb and cruise. There are NO redeeming qualities  in an over pitched prop. Anything under that 5500 WOT in level flight stresses the engine and you lose climb, cruise, fuel economy  and have higher oil temps on climb out. In the older crank cases over pitching could cause a crack in the case.

    So the Rotax spec of 5200 at take off usually gets you around the 5800 WOT mark in level flight. ( different aircraft designs can play a part here) So if you get 5800 WOT then you're  on the better climb pitch side. Reduce that to 5600 - 5650 WOT in cruise which is only 150 - 200 rpm lower and is about 5000 - 5100 rpm on take off will give you a good balance between climb, cruise, fuel economy and engine temps. Thousands of owners do this without any issues.

    If you have a heavy plane, an amphib or a need for a better climb prop like a short field then 5800 is a good target. If you have no real need for a better climb pitch then 5600 - 5650 will balance out your performance. 

    As far as higher oil temps there are other things  that cause this and it's not just prop pitch. 

    Thanks, Roger.

     

    I have the Sensenich 3 blade ground adjustable 3B0R5 prop with 912iS. Lockwood told me that my current prop gains a huge amount of RPM between Vy and cruise speed so the climb RPM needed to be set lower than ideal (which hurts climb performance).

     

    The other consideration is that it's an iS and I want to be in max eco mode under 5500rpm. My A&Ps concern with adjusting the prop pitch to increase my climb RPM is then max eco mode would kick in above max continuous power. Is that true that could happen? Max eco engages now at about 5350rpm. RPM in climb is 4650-4730rpm. So I would have to come up about 400rpm on climb in order to be at the recommended climb RPM. Yet if I did that, wouldn't I then be at 5750rpm when max eco engages? 

     

    You said at least 5500 at WOT in level flight is desired, but at what altitude is that recommendation? I presently get 5600 rpm at WOT in level flight at 2,000' and that drops to 5420 rpm at WOT in level flight at 12,000'. And again, only 4650-4730 in climb.

     

    I'm starting to think about changing my prop. Lockwood told me that Sensenich has a new 3 blade prop that was designed specifically for the 912iS and said it’s a huge improvement over the 3B0R5 prop I have now. Lockwood said “The RV 12iS can climb at 5,200rpm and cruise at 5,450rpm (in max eco) with Sensenich’s new 3 blade prop.” So it sounds like the new Sensenich prop has a much lower RPM spread from climb to cruise -- and thus can be pitched more ideally. I came across the E-Props propeller this morning and am leaning towards that as I haven't found one person say a bad thing about it. Sounds like the RPM spread from climb to cruise is even better than the new Sensenich, plus less vibration, less noise, and double the TBO. 


  • Re: Think I need my prop repitched. Any suggestions?

    by » 8 months ago


    I personally haven't  tried or tested the E-Prop, but have some pretty savvy friends that really like it plus good comments on a few other forums. The Flight Design CTLSi in my hangar gets 5600 in level flight and his eco mode seems to be around 5350.

    Altitude has a lot to fo with engine HP / torque and you will lose these as you increase altitude. This is why I ALWAYS say set your prop pitch for your average altitude. A guy that lives in Florida at sea level and never goes over 2K ft. will have a different prop pitch compared to a guy that lives in Colorado, takes off at 7K ft.  and always flies at 10K+ ft.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Think I need my prop repitched. Any suggestions?

    by » 8 months ago


    I personally haven't  tried or tested the E-Prop, but have some pretty savvy friends that really like it plus good comments on a few other forums. The Flight Design CTLSi in my hangar gets 5600 in level flight and his eco mode seems to be around 5350.

    Altitude has a lot to fo with engine HP / torque and you will lose these as you increase altitude. This is why I ALWAYS say set your prop pitch for your average altitude. A guy that lives in Florida at sea level and never goes over 2K ft. will have a different prop pitch compared to a guy that lives in Colorado, takes off at 7K ft.  and always flies at 10K+ ft.

    p.s.

    The 912iS fuel injection does a better job at adapting at high altitudes vs the 912ULS or UL due to their carbs. 

    That said I have friends that have been well over 18K ft. with the 912ULS. Yes the prop pitch should be adjusted. 


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Jonathan

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