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  • Re: DUC Prop pitch

    by » 5 weeks ago


    This is a ground adjustable prop, correct? Those numbers don't add up for a ground adjustable or fixed pitch prop. Static on the ground is lower rpm at WOT than wide open throttle in level flight. I've never seen one switched like this and it's a 200 rpm difference. That's significant. Something isn't right and it isn't the prop pitch. It has to be in either the tach wiring or the rpm gauge. 

    So far the only prop I have seen that has a static closer to in flight WOT rpm is the E-Prop, but the static is still lower.


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


  • Re: DUC Prop pitch

    by » 5 weeks ago


    Hi Fred,

    your case shows that the „tied down test“ has its limits and also that different props show different behavior. It surely is good as an early indication. However, you are on the right track. Commence the flight testing and adjust the pitch to your personal preferences (balance between climb and cruise performance).

    For the sake of confirming that a perceived „sweet spot“ is „your perfect setup“ I‘d further reduce the pitch a bit and test fly again. If results feel surprisingly better repeat. Once results deteriorate go back to the previous setting and relax. With 5470 revs at WOT in flight you may be pretty close to a good or very good setup already. 
    However, I can confirm that an extra 200 revs at take off can make a big difference (without spoiling cruise performance).

    A quick glance to electric model flying (high performance) helps to say good bye to the tied down test. Many years ago when vertical climbs at 50 meters per second used to be top notch the highly pitched props had no grip at first (when launching, hand-start). But once the planes reached a certain speed they delivered.

    Regards

    Peter


  • Re: DUC Prop pitch

    by » 5 weeks ago


    Hi All,

    DUC SWIRL-3 is a special design trying to achieve "constant speed" effect on ground adjustable prop. Here it is rather not achieved with blade deformation (aero elastic effect with rising RPMs) like in e-Prop or Peszke. It is more complicated here. Have a look into the instruction.

    You can find the following sentence: "To take off, it is not recommended to throttle, brake applied and then releases the brakes. You must put the throttle gradually, brake released. The propeller has a constant speed effect, so this second way avoids cavitation takeoff. Furthermore, this method allows shorter takeoffs.".

    What it means? It means that DUC at WOT at "static" is slightly stalled in some areas on the blades!

    I have SWIRL-3-L and 912UL on my KR-030 Topaz. Static RPM 5400, WOT at flight 2500ft 5700 (~115kt), BUT 5200 RPM at WOT at climb @55kt!. Pitch 19,5.

    So static WOT RPMS are NOT such a simple indication for DUC SWIRL like for other props (I have mounted many of them).  

    My suggestion: begin with instruction initial suggestion from chapter 2 (Applications) with the table there, then follow chapter 7 (Indications for testing) keeping in mind Roger's famous balanced prop in flight setting advices.

    Instruction link: http://www.duc-propellers-usa.com/client/document/dh_sw3_be_02_b-swirl-3_instruction_manual_1019.pdf

    Happy flying!


  • Re: DUC Prop pitch

    by » 5 weeks ago


    Like I mentioned the E-Prop static is very close to in flight rpm. I'm not familiar enough with this Duc.So it looks like more than one prop Mfg is redesigning and changing prop performance compared to the more regular prop design. There's getting to be some many different props out there anymore it's hard to keep up on specs.


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


  • Re: DUC Prop pitch

    by » 5 weeks ago


    Fred,
    I agree with Peter and Stephan. With some installations the DUC, with higher pitch settings, is very inefficient (partially stalled) during a static test and can have substantially higher static RPM than it will during takeoff (once the aircraft is moving). Essentially, the angle of attack is too high during a static test, but the relative angle of attack decreases as forward speed increases. 

    Try a lower pitch settings, it may be that your static RPM will actually be lower with a lower pitch setting because the blade will be more efficient in a static condition.  I have a DUC Flash 3-blade and it works great with the right settings.  I’m set for 5560 WOT at 3500’ level flight.  That gives me 5150 at takeoff.  I don’t remember exactly what static is, but I believe it’s about 5300.  This ended up being at 23 degrees, which is almost the low extreme of the DUC recommended settings. If you can’t get it set up to your satisfaction, call DUC, they are a good company. 


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