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Old Feb 26, 2011, 03:05 PM
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There are several reasons for the high number of tests with GWS HD props...

1) they seem to work well and produce decent thrust from RPM/watts-in

2) they are lighter than APC E. Since my test set up is limited to about 400W, I'm not going to need a prop which can survive 1000W and 50,000rpm... so I have no need to use APC E purely for safety reasons, as long as if I'm not exceeding the RPM limits of the GWS HD.

3) my primary concern is testing motors, so by using the same brand of prop on every motor, I get consistent and directly comparable results.

4) yes, I do test other brands of prop to see how they match up... but in most cases I test 'em against GWS HD... so the "number of tests for other brands" makes no inroads into GWS HD's lead in the "race".

5) I have tested various SF/RS props, but in most cases they are severely "RPM limited" so they are not suited to such a wide range of applications (within my 0W-400W range) as are GWS HD, APC E and EMP.
Hi
a) Testing several motors on the same prop-same rpm (could be one GWS as a reference) is GOOD
b) Testing several props (same PxD) on the same motor-same rpm is not significative if you check only static thrust
* Power absorbed is function of the product Static thrust x air speed for transparency (or pitch speed)
* Static thrust is also depending of blade area
Louis
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Old Feb 26, 2011, 03:07 PM
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Jack,

I wish they would be more specific.

That 165,000rpm/diameter might apply to their IC props and maybe some of their stronger electrics (like the G/F 3 series), but I feel it is far too high for their Electric Only series.

Cheers, Phil
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Old Feb 26, 2011, 03:12 PM
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b) Testing several props (same PxD) on the same motor-same rpm is not significative if you check only static thrust


For that scenario (different brands of prop, of supposedly same diameter and pitch) I measure power-in as well as thrust.... the unknowable variable is "how does actual pitch relate to what is printed on the prop"......so THAT is a problem!
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Old Feb 26, 2011, 05:13 PM
Jack
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Originally Posted by Dr Kiwi View Post
Jack,

I wish they would be more specific.

That 165,000rpm/diameter might apply to their IC props and maybe some of their stronger electrics (like the G/F 3 series), but I feel it is far too high for their Electric Only series.

Cheers, Phil
I only mentioned them as another company that does publish a spec. I don't have any feel for their qualities and haven't flown with any of their props. I have one 5" MA prop that was static tested once but has never been flown.

Jack
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Old Feb 26, 2011, 07:07 PM
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Fair enough, Jack. I just think that MAS produces an extraordinarily large variety of props, made from all sorts of materials, and to offer a blanket "165,000rpm/diameter" for every single prop in their inventory (large/small, electric/IC, slowflyer/pylon, nylon/wood, 2-blade/multi-blade) does not advance the cause of science or safety.
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Old Apr 12, 2011, 07:38 AM
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Hello!

Thanks for this interesting discussion; it helps me a lot to understand our brushless, especially when I try to find the power out.

Looking at your large props database I was thinking if you might want some wind tunnel figures.
It’s quite uneasy to collect such things; the test range isn’t very wide (up to 60 km/h, max prop diameter of 10 inch)… Might be useful to explain a bit more how are the figures collected and used.

Maybe someone else does wind tunnel test ?

But here are some results to show you the thing.

The Ct, thrust coefficient, shows us what happens to thrust when airspeed increases, regardless of prop’s diameter, rpm or air density.

The Cp, power coefficient, does the same for power…

The efficiency is the ratio of “prop power” vs. “motor power out”.

Eff. = Ct*V/nD / Cp

This allows us to compare props of different diameters or at different rpm…

For example, here we see that the APC 7x4 at 12 000 rpm gives a lot more thrust and needs more power than the same at 6 000 rpm (this is corresponding to the exponent > 2 of the thrust/rpm curve in your database).

The max efficiency occurs around V/nD = 0.53 to 0.65. This corresponds to de P/D ratio = 4/7 = 0.57.

At 12 000 rpm the prop is far more efficient than at 6 000.

The graupner CAM 7x4 is quite similar to the APC but looks a bit less efficient at 9 000 rpm than the APC at 6 000.

I’ve tested some other props, lots of them APC.

Guillaume
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Old Apr 12, 2011, 08:52 AM
Jack
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Wow! I think it would be a wonderful to have that kind of advanced prop data online for more props.

The motor testing and prop data that is at flybrushless.com now is wonderful to have and certainly represents a wonderful and generous donation of time and effort by Robert Goble, Dr Kiwi, and a few others.

"..Maybe someone else does wind tunnel test ?..."

The lack of wind tunnels in the RC community is often mentioned here. The 10" size and 60 km/h limits on your tunnels would cover and work for a lot of the props in the data base. Maybe the proprietors would be interested in your data...

Thanks for sharing that, I have to go off and study it to see if I understand it all.

Jack
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Old Apr 14, 2011, 08:48 AM
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Here are some wind tunnel tests:

http://g.rouby.free.fr/Recherche.htm

APC 7x5E, 7x6E and 8x4E.


thrust = (1000/9,81) * ( Ct * rho * (1,225 at sea level) * (rpm/60)^2 * (diameter * 0,0254)^4 ) in g.

power = Cp * rho * (rpm/60)^3 * (diameter * 0,0254)^5

I know it's kind of rubbish...



V/nD can be use this way:

Want to know thrust at stall speed?

V = stall speed = 10 m/s (for example)

n = 12 000 tr/min = 200 rev/s

prop diameter = 7" = 0,1778 m

V/nD = 10/(200 * 0,1778) = 0,28

At V/nD = 0,28 , Ct = 0,11 (APC 7x5)

So Thrust = 1,2 * 0,11 * 200^2 * 0,1778^4 * 1000/9,81 = 538 g.

Might be a little more because of the 12000 rpm instead of 10000 rpm...

I not sure it might be useful...

Anyway more props coming next...



guillaume
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Old May 27, 2011, 11:21 PM
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no reg info

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Originally Posted by lake flyer View Post
I registered , but did not get my confirmation email ??
+1

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Originally Posted by rgoble View Post
I'm not sure what happened there. I sent you a pm to verify your email address and I activated your account.

Robert
I had the same problem.
ajbaker@netzero.com
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Old Jun 09, 2011, 10:51 PM
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Sorry for being out of touch for the last month or two but my kids have been keeping me pretty busy.

yomgui, I think adding the wind tunnel tests to the site could be very useful. I will try and find some time to sit down and figure out the numbers and how I can add it to the site.

If anybody else is having problems not getting the registration emails please let me know. I found a few accounts from early May that were never activated but they are mixed in with others added at the same time that were. That makes me think that spam filters are catching the messages for some people. I know I had an issue with comcast blocking emails from the site before but I think I have that one fixed now.

Thanks,
Robert
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Old Jun 10, 2011, 05:50 AM
Jack
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Nice to see you found the time, Robert.

And if it is not clear from the hit counts or whatever, you page has become one I visit and refer others to frequently. I love the way you can approach the data either from the props or motors viewpoint and the way the data is cross referenced. It is a very useful site for choosing power system components and for helping newbies to understand electric power systems.

Good job!

Jack
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Old Jun 25, 2011, 01:32 AM
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Hello Gents, I like to find out specs for "Extreme Flight 5020/220" motor, I only got some very basic info, if anyone got more info or some experience with this motor I would like to hear it, Thanks Joe.
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Old Jun 25, 2011, 07:16 AM
Jack
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Hello Gents, I like to find out specs for "Extreme Flight 5020/220" motor, I only got some very basic info, if anyone got more info or some experience with this motor I would like to hear it, Thanks Joe.
It should be called a "Torque 5020/220" motor probably, and there does not seem to be any info on that motor yet on the Extreme Flight pages:

http://www.extremeflightrc.com/store...ort=20a&page=1

That motor has been around or mentioned in various posts and threads for over 1-1/2 years or so, you'd think they would be doing a better job on trying to sell it.

Jack
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Old Jun 25, 2011, 04:47 PM
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Quote:
Originally Posted by jackerbes View Post
It should be called a "Torque 5020/220" motor probably, and there does not seem to be any info on that motor yet on the Extreme Flight pages:

http://www.extremeflightrc.com/store...ort=20a&page=1

That motor has been around or mentioned in various posts and threads for over 1-1/2 years or so, you'd think they would be doing a better job on trying to sell it.

Jack
Thanks, that's about all info I got so far, Joe.
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Old Jun 26, 2011, 03:58 AM
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Hi,

I started a thread few days ago, about prop's wind tunnel tests:

http://www.rcgroups.com/forums/showthread.php?t=1457382

I'd be happy to have suggestions about building a tool using the data (excel sheet?), maybe with flybrushless motor's data (if that's allowed).

guillaume
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