Cutting to the chase; the new 11x4.5's are under-pitched - but a recovery plan is place.

BACKGROUND:
Last spring my brother Dave took one of the APC 13x4.5 E-pushers and modified it to 11": clipped the tips, reshapped the blades to match the 11x5.5 and thinned the blades a little.  The result was a very successful prop that he used on the Hellcat profile seen by the masses at Brodak's this past June.  That bird cruises along at 5.5 sec laps and about 9850 RPM.  Based on that success I asked APC to make the new 11x4.5 as a regular production commodity - which they did - for the minumum 200 prop launch order commitment.  I commited to the 200, then offered these up here on SH and the ECL community responded by buying about 130 of them, my break-even point was 137 so that's not too bad...

Unfortunately we have just discovered that the production prop is MUCH different than the prototype.  BTW if YOU have tried the 11x4.5, I would appreciate if you could report your experience and final RPM settings here too.  That would help flesh out the database.  I have not heard back from a lot of people but I have heard the following:

* John Witt reported here that he is running roughly 11,200 RPM on his Vector, and (I think) his Panther.  John also reported that the prop works very well.   (proving the prop will work if you spin it fast enough)

* Keith Renecle reported turning 11,800 RPM.  Keith flies at 6000' elevation so I did not really know what to make of his experience, but I was surprised to hear he was spinning THAT fast!

* Bob Branch reported that he ran out of RPM (around 10,800 for his set-up) before he could achieve a usable flight speed on his Oriental.

* I have not been able to fly this year, but Dave flew the Hellcat again last weekend: in a back to back comparison of the new produciton 11x4.5 versus his prototype.  With the production prop he was flying 6.6-6.7 sec lap times, with the prototype prop it was back down to 5.5 sec laps.

That last back-to-back comparison clearly pointed to the culprit - Dave revamped his Prather pitch gauge so he could use it for the pusher, and got the following comparison between his prototype 11x4.5 and the production 11x4.5:

                      Prototype                       Production 11x4.5E-P
Station        Pitch  Thickness                       Pitch  Thickness
3                  4.5       .105                           4.5        .147
4                  4.5       .106                           4.0        .136
5                  4.25     .105                           3.6        .132
6                  4.25     .106                           3.6        .122
7                  4.25     .104                           3.75      .110
8                  4.5       .100                           3.75      .100
9                  4.5       .092                           3.75      .087
10                4.5       .087                           3.75      .070
11                4.5       .070                           3.75      .053  
 

The difference betwen John W's 11,200 RPM using the production prop on his Vector, and Dave's 9,850 RPM using the prototype prop on the Hellcat is almost 14%.  The difference betwen the expected 4.5" pitch and the actual 3.75" pitch is about 17%.  Given the difference in airplanes & localities, that is a fairly close approximation affirming the magnitude of the pitch problem.

RECOVERY PLAN
I shared this information with APC and they instantly agreed to make things right.  APC is a fine company to work with, this just reinforces that opinion.  There was a big concern about how to segregate the "old" (current" 11/4.5's from the "new" (pending) and we came to this solution.  APC will simply create a mirror-image duplicate of the current 11x5.5 tractor.  Those of us who have used the 11x5.5 know it is a very good prop.  While I am fond of the lower pitch I can cheerfully live with a mirror image of the 11x5.5.  Assuming all goes well we should have replacements in about a month:

* APC is sending me 200 new 11x5.5P's in bulk, without packaging, but the size is molded in place.    

* I will send the new 11x5.5's props as replacements to all who ordered 11x4.5's from me before - shipping costs are coming out of my pocket.  This problem was not my fault, but it was not yours either.  I am NOT too proud to take donations or new orders tho..!

* For those of you who bought 11x4.5's directly from APC (Andy B?) I recommend you wait a few weeks (watch this space) then contact APC and make your own arrangements for replacements.

* I hate throwing usable stuff out.  As John Witt's and Keith Renacle's experience shows, there is nothing really preventing us from using the under-pitched prop, as long as we know what it is and act accordingly.  Instead of setting up around 10,000 RPM we will have to be capable of turning around 11,500 - plan on flying around 11,200 RPM. If you are using 4S pack then I would recommend at a minimum kv=1100, might get away with 1050 but 1000 is probably too slow.  Ironically enough, I am completing two IC-to-ECL conversions that use 4S & 1100 kv motors.  I thought I was going to be "too tall" on kv but now that I know what I'm up against this should actually work out pretty well.

* With the above in mind, I am going to mark my 11x4.5's as 11x3.8.  I suggest you do something similar to yours.

* Finally, anyone who did not order 11x4.5's (sic, 11x3. from me before, I still have about 40 of those plus I anticipate having the new 11x5.5's in a month or so.  Props will be $4.75 and shipping to lower 48 via USPS Prioity will be $5.50 (sorry the average shipping seems to be creeping up).  International orders, by PayPal at actual shipping cost for (most likely) at 1st class-parcel rate as before...

I could have done without the drama, but all things considered, I think this is a very workable plan.  Besides, I can think of at least one famous east coast twin-builder who will be happy that he can get the APC 11x5.5.s in RH & LH flavors! (now git-er-dun, Bobba!)

Hello Dennis,

I tried one of the props a couple of weeks ago on my plane and at max RPM of 11000 it was way too slow, as I have a competition this weekend, 25th September, I went back to the 11x5.5 so as not to have to change trim and setup this close to a competition.
My thinking was after the contest I would fiddle again by re-pitching one of them a little and try again.

I will send you an email too.

Lionel.

Hi Dennis,

I only just tried one of my 11x4.5Ps last Sunday on my Vector and I am so glad to read this. Kind of.   

I have been using the 11x5.5T and was doing ~5.3 sec laps at 9,500 rpm on 61' lines.  When I put the 11x4.5 Pusher on, I left the rpm setting at 9,500 and put on slightly shorter lines ie 60'  expecting it to still be slightly slow. ie maybe 5.7 sec laps.  To my amazement it was doing 6.52 second laps and had bugger all line tension and unable to even do a loop.  I certainly never expected it to be that slow and felt that the prop might be under pitched.

I up'ed the revs to my highest setting I could on the field of 9,900 and it only changed the lap times to ~6.25 secs.  I know that with the 11x5.5 tractor I was using around 2000mAh of 2650mAh battery so could not afford to use any more power without increasing the battery size to 3000.

I figured I was going to need to up the revs to somewhere around 10,500 to 10,700 to get 5.4 sec laps desired so I decided I would not continue to play with this prop on this model and wait to try it on another model.

Your posting certainly confirms my feelings that the prop is under pitched.

I am happy to assist by paying the cost of the postage to Australia for you to resend me some of the new 11x5.5 Pushers.  I am certain they would work well for me.

I really appreciate your efforts in the development of ECL and especially the assistance you have provided me.

Best Regards
Warren

I have to say I'm so glad you posted this here. I was going to post my findings in the original thread but thought I would just be shouted down and it was all my lack of experience. I have 6 of these (Went 50/50 with Pete Beddows to save on postage to the UK). I went a complete afternoon , upping the RPM until I ran out of governor with my Motor/Battery combination. I ended up at 11,800 rpm before I reached anything like a lap time where I was prepared to attempt any overhead manoeuvres. Having lost decent governor input by then I eventually put them away and went back to my trusty APC 11*5.5 tractor set up and decided to put it down to experience..

So... Perhaps I'll substitute my Scorpion 3014-16 for my AXI 2820-8 and give it another try, based on what I found and peoples notes above. The Kv of the AXI should put me right back in the ball park..

TTFN
John.

Thanks for the comments, IM's, & emails.  I really appreciate all the support you are showing. 

John H - Please do not feel shy about posting results.   My first electric would not START (sheesz) and the group here traced it to the arming switch.

Tim S - HOW COULD YOU DO SUCH A THING???  Just teasin, I would'a done the same in that situation.     The new 11x5.5P should be great on your T-bolt and Magician.  BTW when you see here that the new props are available I suggest you contact APC directly about replacing the others you got.

Darrell: Thanks for the update.   

Just a quick update:

I just received 10 test samples of the new 11x5.5P.  Intent is to measure and fly these, THEN approve the delivery of the rest, and send those out.  They look really good however we intend to:

* Measure on pitch gauge, both the RH & LH versions
* Fly both back to back on the Hellcat

Assuming all goes well I will ask for the rest of the samples and start shipping them.  Please be patient just a little longer...

No problem.