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Old Jul 21, 2011, 01:57 PM
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Antony (France)
Joined Sep 2003
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Originally Posted by eJets View Post
@Furdan
your bench testing must not necessarily generate better results than the munufacturer data as the manufacturing process it self leads to a statistical spread - to take this spread into account and smoothen the manufacturing spread you should have tested at least 5 to 10 motors of the same type - did you?
the mean figuers of the manufacturer resulting from tests over more than one motor of the same type - this is how the quality testing of the mufacturing process is done....

The Iron Loss is only indirect related to the RPM - It is related to the magnetic Cycles and these depends not only on the RPM but also on the numer of magnetic pols.
Further more the CC eCalc does extrapolate the Iron Loss (Io) from the mesured mag. cycles (@ Io Voltage) to the effectiv mag. Cycles (at operational Voltage) by using an adequat mathematic model.

nevertheless your Calc is also well done.....

cheers eJet
Hi eJets
Question 1: Yes, I have tested only one sample
Anyway some data from some manufacturers are not accurate
Question 2: For a given motor, the number of magnetic poles is fixed
Louis
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Old Jul 22, 2011, 10:27 AM
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near Zuerich - Switzerland
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Dear Furdan,

your right some data are not accurate as they could be. I observe that they get better and better.
In general - Quality Motor Manufacturer deliver Quality Data.

The Customers are not dumb - If a manufacturer publish "sugarcoated" data the RC community in the forum will unveil this cheats.
So, the publication of inaccurate data does harm the manufacturer most....

cheers Markus
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Old Oct 31, 2011, 06:17 PM
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This prop stall business...how serious is it in actual use? I find myself needing to go to square props (e.g. APC-E 12x12, 14x14) in the calculators to achieve decent (80mph +) pitch speed at low amps for the scale warbirds. Also, how closely does pitch speed correlate to actual flight speed, realizing that variables such as available thrust and airframe drag come into play.

Finally, P-Calc (brantuas) seems to deliver massive thrust numbers. How accurate is this program?
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Old Oct 31, 2011, 11:42 PM
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Pitch speed on the bench and actual flight speed have no direct correlation; I have some models that won't break 1/2 pitch speed in a vertical dive, and some models that defy hobby grade physics by traveling in steady level flight at 10-15mph faster than pitch speed on the bench.

Bottom line... relying on equations to accurately model drag of a real model aircraft is just not practical, and unless you can do that (CFD/CAD?), then bench pitch speed numbers are only good for rough comparisons (ie. 'if that prop has the same thrust and more pitch speed, it should be faster'). Trial and error testing, and referring to archived data is way a more efficient means of arriving at the best prop choice.

I haven't checked out P-Calc, but Drive Calculator numbers are always very close to the thrust I measure on my stand. Lot's of folks with thrust stands have verified DCalc's accuracy. There are some prop constants that aren't modeled as well as others, but overall DCalc tends to be on the money for what I do.

Cheers,
Kev
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Old Nov 01, 2011, 03:24 PM
Rangers Lead the Way
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Thanks Kev. Time for me to crawl out of the cave and buy some props to try out
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Old Nov 01, 2011, 07:02 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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A little better choice for getting rough estimate of static thrust capabilities of various props and at various RPM's is to look them up in the FlyBrushless.com prop database. That will give you some real static thrust numbers that were taken by nice guys that also have some credibility here.

Some don't like to use or even look at static thrust numbers, I consider them to be better than knowing nothing at all. And a good startor intermediate step in the process of finding a good prop.

Jack
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Old Nov 02, 2011, 06:14 PM
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Quote:
Originally Posted by TTRotary View Post
This prop stall business...how serious is it in actual use? I find myself needing to go to square props (e.g. APC-E 12x12, 14x14) in the calculators to achieve decent (80mph +) pitch speed at low amps for the scale warbirds. Also, how closely does pitch speed correlate to actual flight speed, realizing that variables such as available thrust and airframe drag come into play.

Finally, P-Calc (brantuas) seems to deliver massive thrust numbers. How accurate is this program?
With a square prop your acceleration is probably pretty poor.

I would look at the whole power system and select the right battery voltage, motor, ESC & prop combo to reach the desired speed.
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Old Nov 03, 2011, 04:10 PM
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Meaning if you needed to throttle up to get out of a bind (e.g. you start to lose control of a low hover and need to fly out of it?)
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Old Nov 03, 2011, 06:30 PM
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Meaning if you needed to throttle up to get out of a bind (e.g. you start to lose control of a low hover and need to fly out of it?)
Well, for my style of flying yes ... but I was assuming you were sport flying it.

I really meant just accelerating for take off, or throttling up for a missed runway pass etc. The higher the pitch, the longer rollout you will need before you reach flight speed on takeoff or the harder you will have to hit the throttle on a go around.

I don't think I could even hover a plane with a 12x12 prop. I was trying to hover a 10 pound plane with a 70" wing span and a APC 20x15 prop. At full throttle it would just barely hover. I primarily used that prop for high speed precision acrobatics. It was also sucking down over 3000 watts at full throttle which would kill the battery pretty quick. I wouldn't hesitate to use it for sport flying though. Even at a 4:3 ratio of diameter to pitch it was pretty soft on takeoff and needed quite a bit of throttle and additional runway. At a 1:1 ratio, I imagine it is an even softer rollout.
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Old Nov 05, 2011, 12:47 PM
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I see...I think. Should I think of a coarse prop as a high gear...low torque high speed?
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Old Nov 05, 2011, 05:32 PM
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Originally Posted by TTRotary View Post
I see...I think. Should I think of a coarse prop as a high gear...low torque high speed?
Exactly!
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Old Apr 18, 2012, 07:03 PM
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France, RA, Cormaranche-en-Bugey
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Hi,

Here is the link to my calc (excel sheet):

http://g.rouby.free.fr/tetacalc.php

and the link to my site, where I'll try to write some tutorials, if needed... and if you want to post some comments:

http://aerotrash.over-blog.com/pages...r-6330077.html

My calc works fine with any excel version, and can be used with open office (but without macro).

The purpose of this calc is more like power system optimization, so it might be uneasy to use but can be very accurate.

The electric motor model is similar to Drivecalc's model, but it can also work with a simpler model (like eCalc's model).

The propeller's performance is computed from wind tunnel data (mainly from UIUC website).

- simple aircraft aerodynamics,

- 160 motors database, with accurate motor model, or...
- generic motor model,
- simple motor model (from Kv, Io and R),

- 100 + propellers database,
- in-flight thrust and power, efficiency...

- etc, etc...

Please try it ! nothing commercial about this, just sharing and hoping someone has idea to improve it.

Guillaume
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Old Apr 23, 2014, 09:30 AM
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USA, IL, Oak Lawn
Joined Apr 2007
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the issue I have with ecalc is that even if I put in the req setup by the motor manufacture it always comes back that either watts to high or amps to high.
Example is rimfire 50cc 22 x 8 prop on 12S 30/45C batterys. You get this.
Motor @ Maximum
Current: 161.14 A
Voltage: 40.39 V
Revolutions*: 8707 rpm
electric Power: 6508.9 W
mech. Power: 5976.2 W
Efficiency: 91.8 %
est. Temperature: 74 C
165 F
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Old Apr 23, 2014, 12:16 PM
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Joined Aug 2013
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Max surge current for motor is 135, max cont. is 110. Your setup pulls 160+. So you get a warning. Simple to understand that isn't it?

Either e-calc is not calculating right, due to incorrect parameter input, or manf is lying about capabilities of the motor.
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Last edited by Mike Dubovsky; Apr 23, 2014 at 12:23 PM.
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