I have compared both the 13 x 4.5 and 5.5 thin pushers. (Not cut down).

The plane is 70oz ready to fly. (680 square ins).
With the 4.5 the RPM is 9600 for a 5.5/sec lap time
The 5.5 is 9200 RPM with a 5.45 secs/lap.
However, the 5.5 flies the plane slower through the maneuvers than the 4.5 prop does even though the lap times are faster on the 5.5 pitch prop.
The 5.5 pitch prop smooths the corners out slightly and tracks a little better but I feel the 4.5 pulls it through the pattern better.
I notice a bit of noise from the prop in the corners, but it's ok.

It just works!!

Hi Crist
That is a tough question, made tougher by the observation that not everybody sees the exact same result.  I will speculate:

* First assumption is that we are comparing only governed systems but not comparing the governing systems themselves!

* The 13x4.5EP Thin Blade is lighter than the 13x5.5 thick blade and has less inertia. Thus it is possible that it responds more quickly to throttle "bumps" (up or down) and recovers RPM more quickly when doing square corners.

* The 13x4.5EP Thick Blade probably weighs near exactly the same as the 13x5.5EP Thick blade so weight & inertia effects should be pretty much the same.  However the 4.5 has to turn higher RPM than the 5.5; My opinion is that higher RPM is better when we are trying to climb or brake.

* So why do some set-ups exhibit differences one way or the other?  It could be influenced by the motor size and how loaded it is.  The 28xx motors on 4S turning a heavy prop and running at say 85% of its wattage capability will likely respond differently than a 35xx motor on 6S turning the same prop but only running at say 50% of its rated wattage capabiity.  The larger diameter motors SHOULD have more torque but also more inertia than the smaller motors.

*  The power/airplane also come into play.  I recall your prop tests on the Resolve 570; my take-away from that is that you could fly it with almost any 11"-13" prop and it would have been very successful.   By contrast my 80 oz Strega-beast test bed needs ALL the thrust & braking the prop has to give!


I do not have data to back this up, but a really intense look at ICE datalog might shed some light on some of these things.

I do not have data to back this up, but a really intense look at ICE datalog might shed some light on some of these things.

Dennis, attached is a number of logs recorded recently. Shown is RPM during five laps of level flight (left) and at time of the wingover manoeuvre (right) with Governor Gain set to min. respective max. values.

Airplane:  Max Bee  64 oz
Motor: AXI 2826/12
ESC: Castle Phoenix ICE lite 75A
Timer: Hubin FM-9
Timer signal: steady at 1.433 ms (for 9'624 RPM)
Battery: 5S2600 60C
Wheather:  light wind with low gain and calm with max. gain
Propeller: APC 13 x 5.5 EP
RPM set:  9'624
Lap (64ft x 0.015): 5.25"
ICE lite 75 A Governor Gain : Low (15) (Minimum) or Custom (50) (Maximum)  
Head Speed Change Rate: Custom (20)
Motor Timing: Low (0) with min. gain and Custom (2) with max. gain

regards, Peter

Guys,
Excellent stuff!
Peter, I like your engineering approach to this.  Good hard data.   

Hi Crist,
The woof in the corners could be from one of a couple of sources. The prop blades flexing and flapping (helicopter style) is the most likely one.
The next is motor mount flex which turns into a nutating or conical wobble driven by precession.
The two together can rip a motor mount out of the plane. I've seen it happen early on with 3000 Watt F3A setups!

take care,
   Dean p.