fbpx
Login

 

Jump to Forum..

Only 5200 RPM at takeoff (Roger Lee topic)

in 912iS Technical Questions 8 years ago
Hi all (hope Roger Lee will help here)

In our new plane we are fighting to get both water and oil temperature up (have ordered a water thermostat now), but I have been reading on the topics regarding too low maximum RPM on 912iS Sport.

In our plane we get 5200 RPM at takeoff. The airfield is a 70' MSL. I think it can do higher at 2500', but Roger use the term WOT rpm all the time. What does that mean?

The plane use a FITI 2-blade ground adjustable 1680mm (special for 912iS) propeller. I ask the manufacture, and they told me not to touch it.
In cruise I'm running around 4500-4800 RPM (sometimes much lower). 4700 RPM gives around 100 kt.

At takeoff, 5200 RPM really feels like you are starting your car in 3rd gear. Highest I have seen is 5220 RPM :-)

I do value fuel economy, but would at the same time to run with the best possible setting.

If we are to try another pitch, what tool do you need to measure it?

Thanks for all your help here in the forum :-)

Kind regards, Claus

  • Re: Only 5200 RPM at takeoff (Roger Lee topic)

    by » 8 years ago

    Hi Claus,

    I see you have a 1680mm (66 inch prop) ground adjustable prop. WOT means Wide Open Throttle.

    Since you do have a ground adjustable prop you usually want a prop pitch set to get a good overall balance performance. If anyone is over pitched there are ZERO redeeming qualities with over pitching. You lose out on everything. Typically a good rpm be to be setup for for a balanced performance envelope is 5600-5650 rpm at WOT (wide open throttle) at your average altitude in level flight.
    A prop getting 5200 on take seems a little under pitched and would get upwards of 5800 at WOT in level flight. Nothing really wrong with that. That gives you a good climb prop, but you would lose some speed and fuel economy. In other words you'll have to give it more throttle and rpm to do a decent cruise speed which in turn would eat up more fuel. Most guys are around 4950-5000 rpm at takeoff and that usually puts them in the 5600 range, Adding a little pitch back into the prop will also increase temps a small amount. Probably not much in your case.
    Your engine really isn't designed to run its life in cruise at 4500-4800 rpm. It is better to be over 5000 for cruise. Most of the guys I know here have there 912iS prop set up to get that 5600-5650 rpm and cruise around 5100-5400 with the average being 5200. Low cruise rpms is also causing you low engine temps.

    Aircraft Mfg's aren't always right. Rotax and many of us mechanics have proved that many times over.
    If you decide to change the pitch and don't like it it can always be changed back. It takes me about 30 minutes to change a prop pitch on a 3 blade.

    They make a couple different tools, but these two below are inexpensive, easy to use and accurate. The plane does not have to be level.
    level.jpg (You do not have access to download this file.)
    Propprotractor.jpg (You do not have access to download this file.)

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

      
    Report

  • Re: Only 5200 RPM at takeoff (Roger Lee topic)

    by » 8 years ago

    Thanks a lot Roger

    I hope the weather will be good enough for flying tomorrow. But as far as I remember, I only get 5400 RPM at 2500' altitude.
    I have ordered the tool shown on the first picture. Do you have a link for any instructions on how to adjust the propeller?

    Kind regards, Claus
      
    Report

  • Re: Only 5200 RPM at takeoff (Roger Lee topic)

    by » 8 years ago

    I have to leave home right now so I'll try and type something up a little later.

    I just did a Whirl Wind prop on a Kitfox 7 today. It was pitched to get 5850 WOT. Too flat.

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

      
    Report

  • Re: Only 5200 RPM at takeoff (Roger Lee topic)

    by » 8 years ago

    Hi all, new member here.
    New owner of pusher Skyboy 100 HP ULS with 3-blade warp drive.
    When I purchased my airplane last summer my engine was spinning during climb up to 5900 RPM at 16° pitch. I learned to fly with full power on take-off.
    After listening to you guys, I end up changing my prop to 18°pitch.
    And this is what I have now:
    - my WOT at 4000 ft. in level flight is 5580 RPM
    - I am moving 10 miles an hour faster, then I did before at 5500 RPM
    - climb with WOT at about 5470 RPM
    - overall, feels like I have much more power, very happy with everything.

    But one question nobody can answer for me. All my local guys here flying with the propellers set to approximately 13° or so. Nobody believes me, that I can get WOT 5580 with 18 degrees. Most of them, however, have a tractor arrangement.

    Maybe my propeller doesn't get enough fresh air and it's normal for Pushers!?!?

    And one more thing:
    - when I was installing my T-stats (oil and coolant) made phone call to LEAF. They recommend every day cold starting procedure: with ignition OFF turning engine with starter until you see oil pressure 30 PSI min. After that you can turn ignition to ON and start your engine.

    So, why I see everybody turning engines by hand and listening for something in oil tank???

    Thank you Roger for priceless information!!!
      
    Report

  • Re: Only 5200 RPM at takeoff (Roger Lee topic)

    by » 8 years ago

    Hi Eugene,

    Prop degrees will be different for different props and pushers over tractors. That's why we set our own and tweak it for each plane.

    Glad the pitch change is working out for you.

    Just a suggestion:
    After a big prop research project I did I would recommend (if you ever decide to change props) a different prop over the Warp. Warp gave me the same level cruise speed, but compared to all the other props I tested it was the worst in climb by quite a bit. I'm sure it has to do with the blade design.

    Give them a call and ask them why.
    Those are really nice people there.

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

    Thank you said by: Eugene Klimenko
      
    Report
You do not have permissions to reply to this topic.
Related Topics
Title Category Replies
Seeking Advice on MAP and RPM Limits for Rotax 912ULS (Post-SB-912-079) 912 / 914 Technical Questions 2
912is rpm drop 912iS Technical Questions 27
RPM Drop in 912ULS 912 / 914 Technical Questions 3
RPM Drop in 912ULS 912 / 914 Technical Questions 21
Throttle calibration and idle RPMs General Tech Discussion 1
Follow Us

Recent Videos

Safety First!

 

To receive critical-to-safety information on your ROTAX Engine, please subscribe to
ROTAX-OWNER.COM

Prize Giveaway!


SUBSCRIBE NOW
to automatically enter this years draw!

Login