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I need some help and ideas. I have a 912is in my LSA with a ground adjustable prop.  My airport is a 100msl and I typically fly 1500' to 8500' on occasions.  A couple times a year I will use an airport at about 5500' msl.  Normal OAT is 50F to 95F...typically is in the 70's  Think..Northern California.

The prop is currently setup for what I think is the best compromise of climb and cruise, but given my low MSL flying normally...more cruise speed would be appreciated.

On takeoff I get 5200 RPM.  Level cruise I see maybe 5570 RPM.  

Now my issue.  At almost any altitude, if I cruise with RPM from 5270-5400 I get high EGT warnings from my display, 1650-1750.  If I go full throttle it comes out of ECO mode and the EGT comes down significantly...but I'm at 5570 RPM.   It's really hard to find a place when I'm out of ECO mode but below 5500 RPM.  Now granted I may only pick up 5-10 knots with more RPM...and more fuel economy.  But sometimes it's nice to get that extra speed.

So that means that I need to cruise at around 5000-5200 RPM...and nothing more.  Perhaps if it's really cold out I might be able to do more but that's not my normal flying conditions.

What are my options?  Someone suggested that I should take a little pitch out of the prop. But I'm questioning that logic.  If ECO mode kicks in at under 97% throttle position, taking out pitch will give me a higher RPM for the same throttle setting.  And that means at 97% I will be well over 5500 RPM.  It will also give me a slower cruise.

I'm thinking I need to put in a little more pitch, maybe 1/2 degree.  Ideally for cruise WOT to be at 5500rpm.  This will give me a little wider RPM range at 97-100% throttle that I can find.   Right now I have maybe 50 rpm to fiddle with to get in that range.

Or maybe I'm thinking of this all wrong and less pitch puts less stress on the engine and it will remain cooler.

I think less pitch will move up the safe lower RPM range from 5270 to 5370 but that also means I can't go WOT and get full rich because it will be over rev'd

I do have the BUDS software and cable...if there is a way to just program the engine to change the ECO mode point from 97% to perhaps 94%??  That would give me the same result without having to spend hours resetting the prop.

Any help would be appreciated.

 

 

 

  • Re: ECO Mode / Prop Pitch / High EGT / Confused

    by » 6 weeks ago


    I am *far* from an expert, but isn't the EGT your problem, rather than the prop pitch? 


  • Re: ECO Mode / Prop Pitch / High EGT / Confused

    by » 6 weeks ago


    Mine runs 1500 F in eco mode, even on 35 C days, and even when the oil cooler was too small and the temp would spend a lot of time in yellow arc. 


  • Re: ECO Mode / Prop Pitch / High EGT / Confused

    by » 3 weeks ago


    Shawn,

    A while back I reduced my prop pitch to get 5150 at takeoff and I immediately noticed a 40-50 degree increase in EGT.  In ECO mode I would get a high EGT warning in level cruise.  My initial warning alarm is set at 1600 F.  Rotax lists the Max EGT at 1742, but for me that's too high and very hard on the exhaust system and other components. I reset my prop for 1/2 degree more pitch to get 5050 WOT at takeoff and this reduced my EGT to about 1540 F in eco cruise, and the CHT remains well within range.  I generally cruise around 5250, and can get 5600+ RPM at WOT in level cruise. 

     CHT represents work done in the cylinders and subsequently transmitted to the propeller.  EGT is generally wasted heat going out the exhaust.  So when you unload the engine and send less of the energy to the propeller you will get higher EGT and generally lower CHT.  Its a bit counterintuitive.  And on the iS engine your only control over the mixture is by going into power mode, which will richen the mixture.  Lastly, the iS sport engine develops its max torque at about 5000 rpm, so I have no problem setting my prop for 5050 at climb.  You do get slightly more HP at higher rpm, but in my experience the overall performance of the aircraft is best at this setting, and the EGT is in a range I'm more comfortable with.  

     


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