Hi Bruno!
Yes ... '78, exactly. 

thanks and later,
  Dean P.

Hello Wayne,
I'd be willing to bet that the Orbit 20-12 is not only lighter but makes more power on the same prop as the Orbit 25-12 due to its higher Kv.
Yes, motor losses might be a bit higher, but if the motor can stand the heat then why carry the extra weight?
Given that you don't want to keep putting bigger props on our planes for trimming reasons, this dictates a lower-bound Kv for a given size and battery voltage.
Sound right, Paul?
Dean

Exactly 
Even if the 20-12 wasn't very efficient, the motor with the higher Kv (just happens to be smaller) will put more power into the same prop at a given voltage, as well as into itself.
Dean

Kim,
Thanks for your expert input.  I realize that lowering the voltage will indeed affect the response of the esc and the response of the motor to those changes.  Since you feel that a higher pitch prop would help minimize the problem, would a motor with a higher kv also help minimize the delay in the response assuming that the voltage is the same and the esc settings are the same?
Wayne

Kim,
Thanks for the explanation.  There "is" always another way to skin a cat and I guess that is why there are so many flyers trying to find a system that will suit their particular flying style and get results that they are satisfied with if any of us can actually say we are "satisfied".  Have a great flying season.
Wayne

Hi Gang,
The old saying that, "There is more than one way to skin a cat" is true both in general and in this case, but choosing whether to start at neck, tail or a leg has to do with your priorities.
Kim is absolutely right when he says that voltage overhead is the key to excellent (not merely wonderful!) performance.

In my not-so bashful opinion, the combination of Kv and battery voltage should be much more than adequate for the chosen propellor and its pitch: so that there is at least 200 Wats per pound available under static conditions.
No, you'll never run that kind of power dissipation in flight, but "my" eventual goal is to end up with power management that will hit close to that figure for tenths of a second in critical places in the schedule.

Braking is improved with lower Pitch: Diameter ratios, especially in runway wind.
The downside is that prop efficiency and noise suffer.
It will make me quite sad if meaningful numbers of Electric Stunt flyers start running prop/pitch/RPM combinations that howl loudly.
(Historically speaking, the tuned pipe setup was largely created in order to deal with the criticisms heard in Hungary that the dominant 60 setups were too loud;
but eventually a fair number of pipe users adopted prop-noisy setups just because they liked the way they flew.)

My take on this is that prop tip velocities should be limited to prevent transonic tip noise (which also limits the prop efficiency loss some) so that RPM times diameter in inches is less than 130,000.
So 13" props should turn 10 grand or less ... Given a lap time and line length, we have a lower bound on pitch, and then it's a matter of picking a motor Kv and battery voltage that runs on 70 to 75% of the battery voltage.

Yes, motor efficiency and peak versus average battery currents will be higher than they could be with a system optimised for efficiency or battery weight but us lunatic fringe types like that!
On the other hand, if you are perfectly happy with a system biased in the "super quiet / super efficient / super light battery / low component stress" direction, then have at it! After all, it still runs great, time after time after time ...

Have I ranted long enough?
Actually, I will be happy to see the whole constellation of setups developed as time goes on, but please let's keep the prop tip howl at bay...
The rule makers bent over backward to make competitive E-Stunt possible, and the justification was and continues to be QUIET.

later Friends,
Dean Pappas

Hi Mark,
Well designed props can even be pushed to 140,000 rather than 130.
These are typically scimitar shaped and twist and resonance free because of their stiffness and blade width, which that makes them heavier than we want.

What is well designed? The scimitar shaped APCs are certainly among the most efficient and quiet out there.
Strangely the E-props APC sells are of somewhat different design, but they sure are light and efficient, and at our sizes and power levels I don't hear any flappy/gurgle-y sounds.
In the 20" diameter and 3 kilo-Watt sizes these problems have cropped up and APC are in the process of making subtle changes (small amounts of added weight to improve torsional rigidity)
The symptom there in F3A is that taking carbon cloth and CA to both sides of the prop actually reduced power consumption and raised W.O.T. ground RPM.  Golly! 

I've never seen the curled or Q-tips used to good effect in aeromodelling, but that's just 'cause I haven't seen a good setup yet. There aren't enough hours in a day, and yet some folks are bored ...
What sizes are offered?

later,
  Dean

Dean,
The props I saw were on something like 40% IMAC planes if I recall, I dont know that I have seen them offered in our sizes, mine was a theoretical question mostly,,

I am on-board with Dean's 130k benchmark.  Some empirical observation on noise - from a guy who wears hearing aids.

* Strega with 13x6.5 APC-E running 8200 RPM (106,600) = very quiet
* Strega with 13x4 APC-E running 11,000 RPM (143,000) = whiny loud
* Strega with 13x4.5 APC-E running 10,300 RPM (133,900) = noticable but not too bad

* Mythbuster with 11x5.5 APC-E running 9000 RPM (99,000) = uh, did you hear something???

So Dennis,
Do the hearing aids mean thatyou hear the highs better than many of us old codgers?
My teenager was demonstrating one of those "mosquito" cell-phone ring tones for me. I just barely heard it in a quiet environment.
later,
Dean

So Dennis,
Do the hearing aids mean thatyou hear the highs better than many of us old codgers?
My teenager was demonstrating one of those "mosquito" cell-phone ring tones for me. I just barely heard it in a quiet environment.
later,
Dean

For me it s mids to highs - like most of the tinkle tinkle musical ring tones.  Also, the test Strega has a sound we have traced to the air ducting. I cannot hear it real time but can hear it on the video playback.  WIth the t-coils active I can hear eletronic sounds - like when i'm driving and engaged the curise control, and I can hear the brake light switch.  Have not tried listening for the PWM signal in the Phoenix tho...

PJ - I'd say your observation is pretty darned accurate!

Looks good