Let met start this off with high praise for my brother Dave and his son Mike.  They have been doing all the measurements and flight tests - THANK YOU.  The results are shown below.

When the prior 11x4.5 prop did not pan out, APC & I had discussed simply making a mirror image LH rotation (pusher) version of the current 11x5.5E  tractor.  The gentleman I spoke with at APC also said that they would do that, but that they have also been redesigning both their old and new electric props somewhat thicker for more stiffness.  Thus the new pusher is made to the new design standard and the 11x5.5 tractor will also be changed to the same new standard - but the new pusher is different than the "old" tractor, like the ones I (and probably you) have been flying.

You might want to re-read the above a couple times!

APC supplied me we a few of the new 11x5.5 pushers 's to evaluate before they throw the switch on the 200 piece launch sample.  All we had to compare to was the OLD 11x5.5 Tractor - which is almost guaranteed to be the same prop you also have been using. I will be getting some of the new 11x5.5 tractors soon and will report on them then.  But for now


First the the tale of the tape.  Here are measurements taken on the 11x5.5 Tractor and the new Pusher:
                
                     PITCH           BLADE THICKNESS    BLADE WIDTH
Station    Tractor   Pusher        Tractor   Pusher        Tractor   Pusher
-------    -------  -------       -------   --------      -------   --------
     2          5.25     5.75           0.102     0.178           0.89     0.928
     3          5.1       5.25           0.105     0.154          1.003    1.003
     4          5.0       4.75           0.109     0.138          1.042    1.048
     5          4.8       4.6             0.11       0.133         1.032     1.039
     6          4.8       4.6            0.103     0.124          0.986     0.997
     7          4.8       4.6            0.093     0.111          0.906     0.917
     8          4.8       4.6            0.086     0.099          0.8        0.827
     9          4.8       4.6            0.076     0.089          0.692     0.706
   10          4.8       4.6             0.064     0.071          0.58      0.587
   11          4.8       4.6             0.053     0.053          0.484    0.465
 

* As you can see the 11x5.5 Pusher pitches out a little lower than the OLD 11x5.5 Tractor.
* The thickness numbers show APC's new design standards.  The the new prop is thicker at the hub and throughout the span of the blade.  This makes it stiffer - and there IS empirical data to suggest that the stiffer blades will lead to lower current draw.
* Blade width and shape is very close to the same, the pusher is just a tick wider.


Next, Dave took some Static Test data, measuring Watts at 9700 rpm:
* 11x5.5 Pusher  Steady State avg 376W  max 380W  (Memo: actual pitch station 5 - 11  4.6)
* 11x5.5 Tractor  Steady State avg 433W  max 439W  (Memo: actual pitch station 5 - 11  4.

Did not expect that much difference, the low power draw of the new prop might have something to do with the thickened blade too.

For comparisons sake, here are the numbers on the Prototype 11x4.5 (cut down from a 13x4.5) and the Production 11x4.5 previously distributed
 * 11x4.5 Prototype Pusher    Steady State avg 400  Max 406  (memo: actual pitch station 5 - 11 =  4.5)
 * 11x4.5 Production Pusher   Steady State avg 288  Max 293  (memo: actual pitch station 5 - 11 = 3.75)


Static data is OK I suppose, but there is no substitute for committing aviation.  The test bird is a Brodak Hellcat about 42oz RTF , Arrowind 2820, ICE50 in Set RPM mode, on 61' lines.
* 11x5.5 Pusher    -  9838 rpm avg - 5.5 sec
* 11x5.5 Tractor   -  9834 rpm avg - 5.1 sec

* 11x5.5 Pusher    -  9936 rpm avg - 5.4 sec
* 11x5.5 Tractor   -  9927 rpm avg - 5.0 sec

* 11x5.5 Tractor   -  9605 rpm avg - 5.2 sec

As an aside, Dave had never flown the Hellcat with a Tractor prop before.  He reports that the Pusher prop generated substantially better line tension, even flying .4 sec lap slower.

CONCLUSIONS:
* It appears that the new 11x5.5 Pusher behaves close to the prototype 11x4.5 that was carved from the 13x4.5.  From that standpoint it is a complete success.

* If you are currently flying a 11x5.5 Tractor, you will need to increase your setting by about 500 RPM to achieve the same airspeed with the 11x5.5 pusher.

* Put another way, you will need to be able to turn it at somewhere around 9,700 RPM - 10,200 RPM of course, your setup may vary.  


I asked APC to go forward with this prop, they will be shipping them to me soon, and I in turn will be shipping them as replacements to those who bought 11x4.5P's.  I am also going vacation for 2 weeks.  Therefore, I expect to be able to start shipping the new/replacement props the week of November 8.

I'm in for a half dozen!
Dean P.

Sounds good Dennis. Thanks for the detailed report and work that went into making that report.

Rob

OK I am back from vacay and had a big box of PROPS waiting for me.  I have more boxes to be used for shipping them out - Frank, tell the weather man to hold off the n'easters just a big longer..!

Alright, I have shipped 149 of the “new/replacement 11x5.5 Pushers.  The following have been shipped (& many have been received by now.  BIG THANKS to all who ponied up & paid postage on the second shipment.

The shipments I have made are shown below.  All I can say is I tried, but my record keeping had gaps.  If you ordered props from the FIRST shipment and your name is NOT on the lists below then please send me a message with your address & number of props to be replaced:

USA Shipments:
Branch, Cralley, DeMauro, Evar, Hampshire, Hook, Howell, Hubin, Hunt, Jacklin, Morris, Paris, Rigotti, Scarborough, Sawicki, Smith, Traxler, Witt, Wong

Overseas Shipments
Allen, Beddows, Boys, Corney, Smith, Leadbetter

Got about 30 more to sell: hope you buy from me, HOWEVER you should be able to order them from APC directly too...

Just an update:
* I still have a couple dozen each of the 11x5.5P and the 11x4.5P.  Price is $4.75 ea plus $5 USPS Priority shipping to the lower 48...

* I do not have any more 13x4.5P's but they are available from APC.

Hi Warren,
The answer is simpler than all this searching: twist-up the 11" pusher until it flies at the desired lap time at 9400 RPM, just like the tractor.
Yes, the reverse pitch prop will take a little care, when twisting, but it's quite easy with a hot air gun.
If you have a reverse pitch gauge then you are in like Flynt.
If not, fashion a simple triangular shaped guage that fits the tractor at exactly 3/4 span and use it to see how you are doing with the pusher.
Wear oven mitts!
take care,
Dean

Hi Guys,
Let's dig some more ...
Warren, when you say that the higher RPM prop used too jmuch power, do you mean:
1) That you had a problem with insufficient voltage near the end of the flight? OR,
2) Do you simply not like high much higher the milli-Amp-hour draw was for a flight? Obviously if you are close to 75 or 80% depleting the battery this is a big deal.

Remember ... and Dennis is THE guy to tell us all about this ... that efficiency falls every time the prop tip velocity rises.
Dean