I recently posted test results with the new 13x5.5EP prop.  The new prop works very well, unfortunately one of the evaluators burned up a motor doing the test.  Since the motor in question is one of the very popular AXI 2826's it is important to do at least a little CSI work.  My conclusion is that the AXI-2826/12 should NOT be used with a 13" prop.


SOME BACKGROUND
If you sort through the List Your Set-Up thread you will see an abundance of very successful set-ups pairing the AXI-2826/12 with the APC 12x6E prop.  This set-up usually runs in the 8200-8400 RPM zone, give or take a little.  One of the evaluators of the new 13x5.5 prop, Rick Sawicki, is using this set-up in several airplanes including a very nice Brodak Legacy.  Rick tried the new 13x5.5 prop on the Legacy and achieved an immediate flight to flight performance improvement, very noticeable even to those of us standing on the outside of the circle.  However that advantage only lasted a couple flights as Rick ended up burning up that motor.  Contributing factors were:

* The 13" prop gives a 17% larger prop disc area than the 12" prop.  This is great for thrust and braking, generating the improvements that Rick saw, but places a very large load on the motor.

* The larger prop also has a substantially lower effective pitch, Rick had to increase his RPM from 8440 (75% throttle) to 9570 RPM (85% throttle) to achieve the same lap time.  Remember that Castle recommends a throttle setting of 70% to 85% for best governor performance.  Thus Rick went from near ideal to maxed out on the throttle AND he has turning a 17% larger disk to do it.

* Rick's Legacy is very nicely built from the kit and retains the usual Legacy chin scoop.  His normal air flow baffling has proven adequate for the original set-up.  However, the cooling system was not up to the new load.

* Just to add a bit more to the toxic stew, the test day was roughly 95 degrees with NO breeze - the prop had to do all the work all of the time.

As a result of the above, Rick measured motor temperature of roughly 160+ degrees after his 2nd flight instead of his normal 105-110 degrees. Thus it is hardly surprising that he burned up a motor after 2 flights.

Because of the stronger pull Rick might have eventually been able to slow the Legacy down a by .1 or .2 sec per lap and still had enough speed and thrust to drive the Legacy through the pattern, he could have probably backed off the by probably 200 RPM.    However, even slowing the motor a couple hundred RPM would have probably just postponed the inevitable.


Rick had has the same power system in s smaller classic model, the Aldrich AG-1 Duster.  Because of prop clearance issue he clipped the 13x5.5 to 12" diameter.  He had to add 1400 RPM (from 71% throttle to 84%) more to get his same lap time, but the motor sounded very happy - the airplane was ecstatic!  Rick graciously let me fly this bird, there was so much pull available I am sure it could have been slowed by couple hundred RPM and never missed it, the battery draw would have then been close to breakeven too.  The throttle setting was higher than I'd like to see tho...


The AXI 2826 works very well when properly applied.  However I want to caution folks that the AXI 2826/12 on 4S is really not up to turning a 13" prop, much less a 13" prop that ALSO is designed to turn 1000 RPM faster!  If you take this motor AND use a 5S pack then the current levels should be lower and you could run around 67% throttle, rather than the 85% throtle position Rick had to use.

* If you are running a AXI 2826 on 4S turning a thin blade 12x6EP prop then you are running a great set-up; but you already knew that.  Unfortunately your world is going to change when you exhaust your supply of thin blade 12x6's.  APC changed ALL of their props to make them stiffer and stronger.  In the process they also changed the airfoil resulting in a lower effective pitch.  The new "thick blade" design has to turn something like 800 RPM more to achieve the same airspeed as the thin blade prop.  This is not good news to AXI 2826/12 & 4S users!

* Speculating; the best answer might be to start with a 13x6.5 and clip it to 12".  This should keep the RPM increment fairly small, and the resulting paddle blade should improve thrust & braking.

* If you are using the AXI-2826/12 on 4S and want to change from the 12x6 thin blade to a 13x4.5 or 13x5.5 you do so at grave risk to your motor.  You will need to:
  > Make sure you have voracious cooling air to the motor.
  > Switch to 5S pack.
  > Always carry a spare motor!

* One other wild card, the 2826/10 is a higher kv wind, on 4S @9500 RPM it will be near its sweet spot. Again, I think the answer is to clip the 13x5.5 to 12", the paddle blade should still deliver a gain in performance.

* As much as I want to sell props and recoup my investment in the new 13x5.5EP I have to recommend that you NOT use it on your AXI 2826/12 especially on a 4S system.

If you take this motor AND use a 5S pack then the current levels should be lower and you could run around 67% throttle, rather than the 85% throtle position Rick had to use.

It is true, but only between battery and ESC ... current to the motor is not equivalent to battery current, the torque of the motor (which will not change if you fly the same prop at the same rpm and you change only number of cells) is relative to the motor kv * average current, so if you add one cell to the battery, you will lower the battery current, but motor current will stay the same, just more chopped, means it can heat even more, since the hearing = IIR and therefore that chppped current can make more heat in its peak. The same problem is also with ESC heating.

BTW the extra inch makes 17% but the power to prop goes with power of 5 of the diameter, so it can be also much more than those 17% ... but also less depending on prop efficiency, model drag, weight etc

Guys,

Looking at the chart for the test of the new prop one thing that is not shown is the static amp draw or the flight time. On my current AXI 2826/10 setup I am running the thin 12x6EP (depitched to 5.3) at 9000 rpm with a static amp draw of 32 amps off a 4S1P 3900 TP lite pack. With this I pull out around 2450 mah for a 5min 20 sec flight. Now I know some don't think that the static amps are useful but I have found that you can get a feel for where you need to be to keep the heat down and battery draw near the 75% mark by watching it. If I load the motor with say a Zinger 12x6P and get up over 39 amps, things start to get very warm and come close to LVC. The prop pulls great but them motor is not happy.

It would be interesting if you could post the amp draws and flight times that match that data just for reference on the new prop.

Best,          DennisT

I  tested the 13X4.5 prop last year and had to turn it at 100% of a 4s pack and had no governing as would be expected. I decided to to go to low pitch props with the 2826/12 system after these tests. I really feel as a result of the testing to turn low pitch props you need to be running a motor over 900 kv to get the rpm and governor operation we expect with 4S systems.  But the 2826/12 can be used into the low 9000 rpm range and still get good performance.

bob branch

Not following this part.  Why would you decide to go with the low pitch if it was at 100% and had no governing ?

Well I got my 13 by 5.5 props today and I was very afraid to try them on my Axi 2826-12 because of the experience of Rick Sawicki.I now believe that with 5 cells it is a none issue. Compared to my 13 by 4.5 thin hub props the only difference I could find was that I required a slightly  lower RPM.I set it at 10,245 , high governor as compared to 10,338 on my 13 by 4.5 and still went a bit faster . Consumption was 1984 MAH for 5 min 30 sec.which is only slightly less than the lower pitch prop.Immediately after landing the temperature of the motor was 112deg.F.,( very nice cool night at 65F ).Almost identical results with both props, but this is the first time I actually heard the prop cavitating on hard corners. For me , the new prop will be a good replacement for the thin hub 13X4.5, when they finally get damaged, no better no worse.  I'm flying a 64 ounce e-Sultan on 67 foot lines at 5.35 sec. laps..Really  fine design and I am so in love with it,thanks Norm. Keith Varley  B.C.Canada

Keith
You may note that I too ran the 13 x 5.5 WEP with my AXI 2826-12 on 5S but my lines are shorter by a foot.  On the Hubin Timer using the "Phoenix new Set RPM" mode I set mine for 9482 checked 9500 on my Tach for a 5.35 lap time.  Power consumption over 26 test flight average was 1475mah.  Besides me being 4000 feet higher in altitude wonder why is the power consumption so much higher on yours?  By the way, you and I came to the same conclusion - good prop.  I received my order last night. 
Glad you still "love" the Sultan-e.
BTW if your Hubin controller doesn’t have "Phoenix new Set RPM" mode you may want to contact Will and get an updated programmer chip for a nominal charge.
Norm

Glad to hear you guys got the props! If you were already running a 13x4.5 then the new prop is pretty much a drop in replacement.  My oncern when I wrote this post was that people needed to know that the 2826 on 4S would not work, I didn't need to hear from a bunch of folks who learned the hard way!

Things that can increase battery usage:
Motor timing set to high ( castle says it should be low)
Gov gain set too high (the correct setting is rarely at max and never at 0)
Flight time set too long
Running full rpm on ground prior to launch
Excess line rake (one guy reduced his usage by 200mah by fixing this)
Excess rudder offet