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Old Oct 23, 2014, 06:05 PM
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Joined Aug 2014
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Perfect thanks, oddly enough I have a 2212-10 that I bought first, bought the 2826-10 thinking it was a bigger motor.

Now I found out they are identical!
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Old Oct 23, 2014, 09:37 PM
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ggrimley's Avatar
United States, SD, Rapid City
Joined Dec 2011
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We are using the 2200 kv motor with the 7x5 prop. In the static test it gives about 25 oz of thrust, but also draws 25 amps. I was afraid that a 6" prop would not give enough thrust.

On the successful flights, not posted, things went well at about 40% throttle
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Old Yesterday, 07:00 AM
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coreman's Avatar
United States, MA, Southbridge
Joined Feb 2010
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I beg to differ. My testing was done suspended on a digital scale with a KV/rpm meter and a wattmeter inline and I found the APC thrust level to be higher in my tests. I also got a higher KV/RPM count. In close inspection you could see the Master Airscrew prop tips flatten at speed. Cutting down a 9" prop WOULD stiffen the blade tips but the initial comment was an 8x6 three blade. You are basically comparing an 8x7. Your mileage may vary.

Quote:
Originally Posted by Daedalus66 View Post
I don't deny that the APC props are more efficient, but the key point is that the three blade 8x6 Master Airscrew props offer a level of thrust for a given KV that can't be reached by any two blade 8" prop. Yes, less amp draw for the two blade, but considerably less thrust too.

I did extensive testing of motors and props for both the Polaris XL and the Ultra. One thing I learned is that static testing doesn't give much in the way of useful results. All mine was done in the air using an Eagletree data logger.

The very best prop for performance on a 3s battery with a motor around 1500 KV was a Master Airscrew three blade 9x7 cut down to 8" diameter.

On the other hand, for a little less speed and climb but significantly less current draw and thus longer flights, the APC 8x6 two blade is clearly superior. But you can get most of the same benefit by just throttling back with the three blader.

Bottom line. I fly my Ultra on 3s mainly with the cut down three blade 9x7. But the APC 8x6E is a perfectly good alternative.
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Old Yesterday, 09:58 AM
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Abbotsford, BC, Canada
Joined Nov 2001
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The problem with static tests are the blades are not passing through the air efficiently, They are "stalled" and "thrashing" the air. Static testing can indicate gross differences but you are basically testing which propeller performs better when it is completely stalled. If you do a lot of high alpha or hovering, that's cool. The fairest test for flying at speed is in the air with something like a data logger.
my $.02
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Old Yesterday, 10:51 AM
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United States, NY, Depew
Joined Mar 2014
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Quote:
Originally Posted by ggrimley View Post
We are using the 2200 kv motor with the 7x5 prop. In the static test it gives about 25 oz of thrust, but also draws 25 amps. I was afraid that a 6" prop would not give enough thrust.

On the successful flights, not posted, things went well at about 40% throttle
Just an FYI....I use the "standard" 2200kV motor with a 6X4 prop and my performance is just fine!! (I've also used a 6X5 prop for a tad more punch, but only bought it because my LHS didn't have the X4 in stock!) take off from grass and has very good vertical climb and plenty of power for loops, rolls etc. That being said on my next build I'll raise the motor mount just a bit so I can swing a 7" prop as well!!
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Old Yesterday, 11:10 AM
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coreman's Avatar
United States, MA, Southbridge
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Quote:
Originally Posted by cayuse View Post
The problem with static tests are the blades are not passing through the air efficiently, They are "stalled" and "thrashing" the air. Static testing can indicate gross differences but you are basically testing which propeller performs better when it is completely stalled. If you do a lot of high alpha or hovering, that's cool. The fairest test for flying at speed is in the air with something like a data logger.
my $.02
Understood. But all are traveling through dirty air so it is still an apples to apples comparison even if not optimum. How is the data logger giving you thrust measurements similar to my digital hanging scale? You are getting load measurements. but not the efficiency of the prop/thrust. All things being the same, if you are flying and get the same numbers going into the motor/ESC but one prop is 72% and the other is 80% efficient, the 80% prop will give you more thrust at the same wattage settings.

Maybe I'm not aware/expecting the same info from the logger you are using/referring to. Are you getting airspeed indications as well? How is it telling you the thrust?
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Old Yesterday, 04:04 PM
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United States, SD, Rapid City
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Thanks for the info NewZee. I will get a 6-4 for my nest flight.
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Old Yesterday, 04:57 PM
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United States, NY, Rochester
Joined Apr 2004
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Quote:
Originally Posted by Daedalus66 View Post
Just stay with the same motor but substitute a two blade 8x4 APC prop and use a 4s battery. That's what I use when I feel a need for speed. Note the need to reduce the prop or you will overload the motor and ESC.

Caution. It will be much faster and you will have to take precautions to avoid control surface flutter. No slop in the linkages is allowed. I lost an aileron when I first flew with this setup and ended up reattaching the ailerons with pin-type hinges. I also beefed up the control horn mounting.

EDIT
Or go to a bigger, relatively high KV motor and suitable ESC and use 3s, as suggested above. Note that the higher current will then require high-C and/or larger battery. You can't get away with 2200 25C, for example. I would not use less than about 3000 30C or 2500 35C for such a setup. The good thing is that the Ultra is big enough to carry a large battery comfortably. You may need to cut out the back of the battery slot to get balance correct.

Either 3s or 4s can work well as long as you make the necessary changes in each case.
The stock esc was not compatible with 4s. I switched to a larger esc, 4s battery, and 8x4 apc prop. No increase in speed. My Wattmeter read 25a and 325w. I tried an apc 8x8 and the Wattmeter read 35a and 520w. More speed but flutter in ailerons.
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Old Today, 08:10 AM
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G550Ted's Avatar
Savannah, GA
Joined Jan 2008
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Quote:
Originally Posted by cayuse View Post
The problem with static tests are the blades are not passing through the air efficiently, They are "stalled" and "thrashing" the air. Static testing can indicate gross differences but you are basically testing which propeller performs better when it is completely stalled. If you do a lot of high alpha or hovering, that's cool. The fairest test for flying at speed is in the air with something like a data logger.
my $.02
It's past time to once again dispel the often re-quoted erroneous statements about props being stalled during static runs. And ""thrashing" the air""?! Ugg, let's try to stamp out the RCG pseudo-science and internet malarkey.

If a prop is stalled it will provide very little thrust. That is not the case with any model or full scale operation that I have ever experienced or aware of from a reliable source. Can there be a region of the prop that may be stalled under static conditions? Perhaps in some cases and certainly in others depending on the particular prop and installation, but that would occur very close to the root which provides little of the total thrust from the prop under any conditions. In any event, there would never be a situation where one could consider the prop to be "completely stalled" as you state.

Another verification disputing the assertion of a stalled prop is the higher power required to turn it at a given RPM under static conditions indicating it is producing a great deal of thrust (lift if you will) and that thrust (lift) is creating more induced drag as a result. We also see that as the decrease in amp draw and increased RPM as airspeed is increased. In fact, properly matched fixed pitch props of any scale produce their maximum thrust at zero airspeed and their thrust continually decreases as airspeed is increased.

It is also a misunderstanding to state that a prop operating at low or static airspeed is "traveling through dirty air". If that were the case it would result in a higher static RPM due to the resulting inefficiency not the lower RPM we consistently see. This is so because the prop is inducing a continuous inflow into the disc and not chopping the same air as some think.

Not mentioned recently but necessary to also address is any discussion about any aircraft propeller "cavitating". Cavitation is the formation of gas bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Unless you are trying to power your upside down Polaris back to shore that simply is a condition that can't happen with an aircraft propeller.

Ted
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Old Today, 11:56 AM
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United States, OR, Portland
Joined Jan 2008
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My Polaris is my only plane with true unlimited vertical (2200kv and 6*4 and 3s 2100mah), it is kind of amazing. It really only has it on a brand new battery, but wow it sure is amazing to take off and climb basically straight up as far as I dare, then flip over for the first high speed pass. Polaris is definitely my most fun plane to fly.
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