It could be prop what is different.

Try to use the same prop, reverse the rotation, reverse also motor mounting, so the prop will spin the same direction. Then you will see if there is a difference.

I am guessing that it isn't possible to tweak the props to the same pitch bu simply twisting at one radius. This adds (I think) a constant angle to the original varying angle, which varies as a function of radius. So if you match at one radius by repitching the lower pitch prop, then its tips will actually be over pitched when compared to the other unchanged prop.

I think the fact that the stock APC pusher is less of a load than the stock tractor shows that it is easy to mess up pitch by small errors.

So that is my WAG!

OK - I ran some tests with my setup that I have been flying all summer.  I tried to set up something that would test Dennis' observation, Igor's suggestion, and my own question above - so I set up a motor/esc on a test stand, charged up a couple of battery packs and ran each prop CW, CCW(by programming) and CCW(by wire swapping).  The props were an 12-6 APCe, a 12-6 APC-clone from HobbyCity, and a 12-6 APCep (pusher).  None had been modified, other than normal cleanup and balancing.  Each run had the prop mounted so that it turned the direction it was designed to turn, and the "CW" or "CCW" in the table refers to the motor direction as seen from behind (ie: clockwise is normal rotation for a tractor prop).

As a final test, I ran the two genuine APC's at 7500 RPM and recorded current using the 4s A123 pack to see if the ESC at partial throttle had any effect.

The hardware:

Motor - Turnigy SK3548-1100
ESC  - HobbyCity SuperSimple 50A (Can program direction, among other things)
         (the timing advance was set at 7 deg., and the freq. at 16 KHz.)
Control - Will Hubin's TE-1 throttle emulator
3s2p 4200mah, 20C Hyperion LiPo
4s1p 2300mah, 30C A123 Pack

         Battery - 3s2p Hyperion, 20c, 4200 mah            
                           12-6 APCe           12-6 Clone         12-6 APCep   
   Dir.               RPM @ Amp         RPM @ Amp        RPM @ Amp   
   CW                8100  39.5          8300  42.5          8400  41.0
   CCW(Prog)      8300  39.8          8500  44.5          8500  42.0
   CCW(Wire)      8400  40.5          8300  43.2          8400  41.0
                     
         Battery - 4s1p A123, 30c, 2300 mah            
                  12-6 APCe          12-6 Clone          12-6 APCep   
   Dir.               RPM @ Amp         RPM @ Amp        RPM @ Amp   
   CW                8400  41.0          8400  44.0          8400  42.0
   CCW(Prog)       8500  42.0          8400  44.0          8500  41.5
   CCW(Wire)       8400  40.2          8400  44.5          8500  43.0
                     
         Battery - 4s1p A123, 30c, 2300 mah            
                       12-6 APCe          12-6 Clone             12-6 APCep   
                            RPM @ Amp          RPM @ Amp           RPM @ Amp   
   CW                7500  25.1             --   --             7500  25.2
   CCW(Prog)      7500  25.2             --   --             7500   25.0
   CCS(Wire)       7500  25.4             --   --             7500   25.1

It seems to me with MY setup, direction (however it is achieved) doesn't have much effect on current or RPM for any particular prop.  The small current differences can be attributed to the battery state of charge and the amount of time I allowed RPM to settle before recording the current and RPM.

I should probably add, also, that both of the genuine APC props were checked for pitch earlier in the year and both pitched out almost exactly the same - pretty much 6 in. of pitch at each station.  This measurement was borne out in my flight results - I've only flown the Pusher a couple of times, but lap times are virtually identical (with no changes in my timer settings) to the tractor version and I personally can't tell much, if any, difference in the flight handling.  I've not been able to notice the difference in performance that other's have written about, but have only the one pusher to use.

One last item that may be pertinent is that this is pretty much your 'basic flight package' - and the above is pretty much the way I fly it.  Cheap ESC, 3 cell battery and an SK Turnigy motor - I can't speculate on how a Governor Mode speed control might affect the performance.  I fly the Hubin timer with the 'throttle advance' feature set to give me slightly faster speed at the end of the flight than at the beginning.

I think Alan is on to something about the props especially if both are modified but (possibly) a little different.

In our tests of 12x6 pusher vs tractor we also concluded that they behaved the same (needed same RPM) Rick Sawicki did the test and concluded that he needed to SLOW the pusher to get the same airspeed as the tractor - this is NOT the same experience that others have reported!

I am wondereing if the flight trim is starting to come into play here.  My supposition is this: the slipstream effects off the pusher increase line tension.  If you have a bird trimmed out using a RH prop then just swap props the effect could be additive to the point where it actually seems like the bird is crabbing o'b and requiring more power to fly.  it takes less power to fly around the circle then to crab out.

When Crist made the change (see his thread on the 570 profile) he noted that his bird seemed to settle down on the end of the lines.  That could be amanifestation of the reversed slip stream.  BUT he also reported having to run a little faster.  I do not recall that Crist ever re-trimmed for the pusher...?

We had the Strega trimmed out with the 13x4 tractor, switched to the new 13x4.5 pusher and ended up moving the leadouts about 3/16" forward.  we have actually run out of room to move any farther forward - unless I can reach in a remove a couple shear webs so the back line can clear.

I guess this is a round-about way of suggesting that when we change from tractor to pusher, the flight trim should ALSO be changed?  Ironically the better the bird is trimmed & optimized for the tractor prop, the more things MIGHT have to change for the pusher.

Yup,
The leadouts move forward, at least that's what Bob and I found.
Dean P.

No Alan,
the reason is this: anything that increases the spiral airflow, like a slowdown in airspeed at fixed RPM or an increase in current and torque as the governor kicks in, will impart more right rudder yaw as it happens. It is the right thing for what happens as you go above 45 degrees. Normal prop rotation will always be in the wrong direction.

The forward leadouts reduce line tension when the plane is moving faster and centrifics are good, but the rudder, right-thrust and now correct direction spiral airflow effects yaw the nose out to help when either the airplane slows or when the governor "throttles up".
I think you had figured this out already!
best regards,
Dean P.