All,

There are many different ways to skin a cat in our hobby.  With the most recent way of flying CLPA with electric power-systems, we have opened up a whole new way of thinking.  We have much more information available through data loggers that can give us absolute positive feedback about how our systems are behaving besides what we feel at the handle. 

One very important thing that has come out is the use of either high or low pitch props.  This is a very debatable issue as to which is best to use.  I have argued that the use of lower pitch props are better.  This is why:

          1.   Increased static thrust per rpm needed to sustain accepted lap times.
          2.   Increased governor effectiveness as small changes in rpm or fluctuations have less effect to airframe speed up/slow down.
          3.   Better overhead line tension as a result of higher thrust in high loading situations.

I have tried several higher pitch props on different size airframes.  I have always gone back to the lower pitch as they have performed better.  Bottom line is that you have to match your airframe requirements & motor/battery selection to what prop is best for your Total System Performance.  I have chosen to go to higher Kv motors as they typically have less resistance.  THIS IS NOT ALWAYS TRUE!!!  It is dependant on many factors.  The motor platforms I use are the 35mm to 42mm class.  (35-42, 35-48, 42-40, & 42-50)  My 4S set-ups are in the 900-1100 Kv range and my 6S is 500-650Kv.  This puts me in @ around 10,000 RPM as the most efficient governor operating range so lower pitch props are the best for me. 

I would like to share my experience with the E-Strega.  The model weighs 80 ozs.  It is powered by an EPS 65 system from Brodak.  We initially flew it with an APC “E” 13 x 6.5.   It flew okay but was a really bear in the wind.  We ended up running @ 7900 rpm to get 5.2 lap times on 66’ lines.  We then changed it to an APC “E” 13 x 4 @ 11,000 rpm.  MUCH BETTER!!  Doing the math, it shows that static thrust (calculated) for the 13 x 6.5 @ 7,900 rpm was 87 ozs.  The 13 x 4 @ 11,000 rpm had a static thrust (calculated) of 106 ozs.  This increased thrust made the airframe fly much better and also made the motor run more in the Castle Phoenix governor’s sweet spot.  We now fly it on the APC “E” 13 x 4.5 Pusher @ 10,200.  This has a static thrust (calculated) of 103 ozs.  The motor seems happiest at this setting.  The added bonus of the pusher prop helped the vertical maneuvers of this heavy airplane too.

Again, this is what I have found to be true to me and the airframes I have flown.  Many have been successful using higher pitch props.  I haven’t.  I say to you, use what is best for your airframe.

I hope that this thread sparks some good conversation on what others have found in there set-ups.  There are a lot of us flying ECL now.  Makes for a great pool of information.  Now, back to the work shop for me.

Archie Adamisin
Muncie, Indiana         

Archie,

I have been playing with rpm settings on my AXI 2826-10, 4S1P 3900 set up with a MAS 3 blade pusher, 11x5.8. I had the pitch down at 5.4 and needed to increase the rpm to 9400. At this setting it pulled 44amps static. When I flew the set up it hit the 5.1 lap time that I was after and flew the ship great. Down side was that it pulled 3450 out of the pack. I reset the pitch to 5.8 and decreased the rpm to 9000, this also hit the 5.1 lap time and flew the ship well while pulling 3125 out of the pack had a static draw of 36.5amps. I like the idea of the low pitch high rpm but I think we need to balance the amp draw and the pitch to stay within the limits of the battery. I seems that at the higher rpm the drag on the prop creates more load than the pitch. Have you tried comparing loads with the same prop at constant lap time and varying pitch and rpm? It would be interesting to see how the APCE -P would load.

Best,            DennisT

Mark,

Good point, maybe Archie can test the different motor prop/pitch combo's to see if there is a better way to pick motor/props. How about it Archie?

Best,    Dennis

I am making a 4.5 pitch prop. And for starters I will go to the Tgy 42-50 650 6S 2600 and a 4.5 pitch prop. I do also believe that a lower pitch prop will also help with the run away too. The advantage of the extra thrust is most evident when you accelerate out of a corner in sharp cornering maneuvers.

If I do the math it looks like I could get by with a 5S battery on this setup.  650KVx3.7x5=12025max RPM  witch is about 80% of max RPM.
Is my math OK?
One more thing here my plane is less draggy and it weights much less than a Strega so i predict to run the motor in the 9800 to 10000RPM range witch will again use less amps.