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E-Prop Pitch


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10 hours ago, DJ Todd B said:

Just looking to see what the E-Prop owners out there have set their pitch to and was it for more Climb or Cruise.  

A properly set E-Prop will improve both climb and cruise over a Neuform.  Pitch it to be ~5500rpm at WOT in cruise at a typical cruise altitude for you.  Do a search on these forums and you should find some people posting their pitch numbers.  IIRC the typical pitch ends up somewhere around 27-27.5°.

Be aware that the E-prop acts a little backwards compared to other props.  Most other props on a takeoff run load up and and have a slower RPM that increases as you pick up speed.  The E-prop is reversed, it starts out at higher rpm and then the rpm comes down as you accelerate.  My RPM is about 5700 when I first go to full power, then slows to about 5300-5400 in the steepest part of the climb, and finally creeps back up to 5500 (at WOT) once leveled out in cruise.

Talking to E-props folks I gather this behavior is because the shape and twist of the blades causes different parts along the length of the blade to be more or less efficient at different loadings and blade AoA, giving what they call their "constant speed effect".

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5500 rpm is optimal. Anything above or below reduces performance, I have experimented with this prior to the prop being approved in the US for FD and approval was based on the data. I am hoping to do the same for the Jabiru 230.

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9 minutes ago, Madhatter said:

5500 rpm is optimal. Anything above or below reduces performance, I have experimented with this prior to the prop being approved in the US for FD and approval was based on the data.

I agree.  Am I remembering right that that's usually around 27° blade pitch?

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9 hours ago, FlyingMonkey said:

I agree.  Am I remembering right that that's usually around 27° blade pitch?

My last repitch was around 26 degress, but that was using the less than accurate e-props level.

 

11 hours ago, FlyingMonkey said:

Pitch it to be ~5500rpm at WOT in cruise at a typical cruise altitude for you

The latest manual now states 5500 rpm WOT at 2500 feet MSL.  I ended up having to increase the pitch slightly to get that.  I was at around 25.5 before that and had to increase to 26 after I saw that in the revised install manual.  I originally set it for 5500 RPM at 5500 feet which is my average/normal cruise altitude.  Don't think it'll make that much of a difference though, as I didn't really even notice a change overall.

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11 hours ago, Garrett Gee said:

My last repitch was around 26 degress, but that was using the less than accurate e-props level.

 

The latest manual now states 5500 rpm WOT at 2500 feet MSL.  I ended up having to increase the pitch slightly to get that.  I was at around 25.5 before that and had to increase to 26 after I saw that in the revised install manual.  I originally set it for 5500 RPM at 5500 feet which is my average/normal cruise altitude.  Don't think it'll make that much of a difference though, as I didn't really even notice a change overall.

Ah, thanks.  Mine does 5500 at 2500ft where I usually cruise when flying locally, so I guess I just happen to be right on the current guidance.  I'm sure you're right, the difference between 5500 at 2500ft and 5500ft has to be minimal, probably less than half a degree.

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The digital protractor that comes with the prop is only good for the first blade, it's too inaccurate for repeatability. After using it on the first blade then use a machinist bubble protractor to match all the blades. A real machinist bubble protractor has extremely accurate repeatability. Bubbles don't lie.

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So, trying comparing Apples to Apples... Since the aircraft, engine and blades don't really know that they are at the altitude of 2500 and 5500 MSL, shouldn't these numbers be taken and tested at the DENSITY Altitude reading instead? Today I was at 5500MSL with A density ALT of 7200.  I don't see how that would be a fair comparison at 5500MSL and DENSITY ALT of 4500'.

When I took at 1400' MSL, My DA was already 3500'.

Your thoughts???

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4 hours ago, DJ Todd B said:

So, trying comparing Apples to Apples... Since the aircraft, engine and blades don't really know that they are at the altitude of 2500 and 5500 MSL, shouldn't these numbers be taken and tested at the DENSITY Altitude reading instead? Today I was at 5500MSL with A density ALT of 7200.  I don't see how that would be a fair comparison at 5500MSL and DENSITY ALT of 4500'.

When I took at 1400' MSL, My DA was already 3500'.

Your thoughts???

Yes the correct target is density altitude.  Setting for a 'typical cruise altitude' isn't precise.  East/West typical cruises vary by 1,000' for example and density altitude is ever changeing.

When cruising and limited to 5,500 and you realize 5,500 @ WOT you are cruising at best speed.  If your throttle is retarded at 5,500 you have partial power and are pitched for best speed at a higher DA. If you'r WOT is less than 5,500 you are pitched for best speed at a lower altitude.

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6 hours ago, DJ Todd B said:

So, trying comparing Apples to Apples... Since the aircraft, engine and blades don't really know that they are at the altitude of 2500 and 5500 MSL, shouldn't these numbers be taken and tested at the DENSITY Altitude reading instead? Today I was at 5500MSL with A density ALT of 7200.  I don't see how that would be a fair comparison at 5500MSL and DENSITY ALT of 4500'.

When I took at 1400' MSL, My DA was already 3500'.

Your thoughts???

Fair point, should be density altitude of 2500 feet MSL.

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  • 2 weeks later...
3 minutes ago, Jim Meade said:

My measurements are about 63 degrees, but I measure it differently.  None if it matters at all.  All that matters is RPM at WOT at the desired altitude.

Ah, yes.  "on the step".  Pass the popcorn.

Assuming you're measuring by the reciprocal of others' measurements, you are right at 27° (63 + 27 = 90).

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Are most of you cruising near max rpm on cross country trips? I still have the neuform prop, but I tend to cruise between 5100-5200 rpm just for noise and fuel burn.

My plane already seems slower than most at about 117 true at 5500 rpm, but I can’t see buying the new prop for just a little more performance. We already out perform most two seat production planes. I’m pretty happy with what I get now. I live at sea level, but it’s not uncommon to see 9000-10000 feet to travel anywhere and get over local mountains.

Sorry to get off the topic of prop pitch. Maybe I’m just hoping someone can help me justify going e-prop!

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1 hour ago, Towner said:

Are most of you cruising near max rpm on cross country trips? I still have the neuform prop, but I tend to cruise between 5100-5200 rpm just for noise and fuel burn.

I like 5100rpm for traveling if I'm not in a hurry, it's quiet and still fast enough with good fuel economy.  5200-5400 is a good range if you're trying to make good time, you'll gain some speed from the higher rpm but the fuel burn will go up.  Above 5400rpm you're mostly just making more heat and noise, you'll gain a knot or two but the fuel burn goes through the roof. 

When I'm just puttering around the local area (honestly most of my flights) I'm at 4800-5000rpm. 

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9 minutes ago, Anticept said:

I use whatever RPM gives me Carson's Number, more if there's a decent headwind.

 

https://www.aopa.org/news-and-media/all-news/2010/december/01/technique-cheap-speed

Hmm...according to that article, the number is found by best glide x 1.316.   Best glide at -6° flaps is 78kt.  So that number for the CT is 78 x 1.316 = 102.6kt.  That is awfully slow...102kt indicated might be a good number at 10,000ft to give a good TAS cruise speed, but at lower altitudes it would not be ideal or even good.  102kt indicated at 4000ft would have me chugging along at something like 4500rpm.

Maybe I'm missing something?

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