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Old Feb 23, 2011, 02:39 PM
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Don't know if the GWS RS 9x4.7 data are mine... but if they are, it is possible that the lower curve is for data from my old stand (perhaps even my old vertical one!), the upper curve might be from data from my "newer" pusher stand.
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Old Feb 23, 2011, 05:03 PM
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Originally Posted by jackerbes View Post
..........
One question I have is about the larger number of points in the APC curve and the fact that the points deviate less from the line than the points in the GWS curve.

Is that a reflection of having more samples for the APC prop and there being less variation in the RPM as the prop was tested? Or is it combination of both of those things?
I think that part of the apparent larger scatter in the one plot is the difference in the vertical scale of the two plots.
The one with the greater Y-axis range looks like more compact data.
If you look at the range of scatter in absolute value instead of percentage of the total y-axis displayed the difference is there but isn't nearly as great as it is at first glance.

Walt
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Old Feb 23, 2011, 05:08 PM
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Originally Posted by Dr Kiwi View Post
Don't know if the GWS RS 9x4.7 data are mine... but if they are, it is possible that the lower curve is for data from my old stand (perhaps even my old vertical one!), the upper curve might be from data from my "newer" pusher stand.
By the way - Phil (Dr. Kiwi) is going to be sending me his spreadsheet when he gets his home computer connection straighted out.
I will take his latest data (vertical test stand) and pull out the info, prop by prop, plot it, and post it over on his THRUST VS. RPM thread.

Walt
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Old Feb 23, 2011, 06:15 PM
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I will take his latest data (vertical test stand)

Ignore anything from the obsolete "vertical stand"... "tractor" is inaccurate...."pusher" is the best I've got.
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Old Feb 23, 2011, 07:13 PM
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Originally Posted by wjbite View Post
By the way - Phil (Dr. Kiwi) is going to be sending me his spreadsheet when he gets his home computer connection straighted out.
I will take his latest data (vertical test stand) and pull out the info, prop by prop, plot it, and post it over on his THRUST VS. RPM thread.

Walt
I can save you some time if you would like. I am working on a page that will let you pick the prop from a list and will show you the chart.
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Last edited by rgoble; Feb 23, 2011 at 11:10 PM. Reason: Removed broken link
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Old Feb 23, 2011, 11:08 PM
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I added a new page to the tools that has a drop down box with all of the props and a graph below it. When you select a prop from the list it will show a chart below it.

http://www.flybrushless.com/tools/thrustCalc

I am now working on to adding a form below the chart where you can input an RPM and it will give you back a thrust based on the data in the chart. I hope to have that done tonight or tomorrow.

Robert
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Old Feb 24, 2011, 07:06 AM
Jack
USA, ME, Ellsworth
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That looks great Robert.

I'll have to study it a little but it looks like it is going to be a wonderful tool.

Do you handle registration there? I have been trying to get it to send me my password and haven't gotten it in a few tries. Can you reset that? If you want to email me I am "jacker at midmaine dot com". Thanks for any help.

Jack
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Old Feb 24, 2011, 04:22 PM
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Originally Posted by rgoble View Post
I can save you some time if you would like. I am working on a page that will let you pick the prop from a list and will show you the chart.
Well before I read this I used Phil's newest ss which had about 900 pusher data points for the 8 x 4 GWS HD and it looked like your plot.
So I took his 2007 spreadsheet and eliminated all of those points from the new set - left me with a little over 450 points. My reasoning was to only use the newer data from his more sophisticated versions of his test bench.
The larger set fit a power of 2 curve (like your curve did) best and the later subset fit real well with a power of 3 (cubic regression). The program I used to generate the regression curve had other terms in it, too.
This plot has a lot less scatter - I would think that that supports the notion that the later data is possibly better (what do you think, Phil).

Here is the plot, below.
I will also post it over on the THRUST vs. RPM thread. Which is here:
http://www.rcgroups.com/forums/showt...3#post17507974

Walt
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Old Feb 24, 2011, 05:55 PM
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Your mathematical expertise exceeds mine, but it looks like a pretty good fit to me. One other reason to exclude early data (other than "pusher" versus "tractor" test stand configuration) is that, early on, I was using an old barn at the school as my test facility with temperatures at ambient (ranging from -5C to +35C!). After that barn was demolished (now a parking lot) operations had to move to my dining table in the apartment... a fairly constant 22C ambient.
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Old Feb 26, 2011, 12:30 AM
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Originally Posted by A Useless Geek View Post
Okay, to return to databases, are we all interested in a prop database similar to the motor one? Collect whatever is available from the OEMs and measure everything else? Do we end up with thrust versus RPM, drag coefficient, max RPM, max efficiency RPM, yada yada yada?

Also, I'd like to see a prop database contain lots of hub information. For instance, all the GWS EP series "slow fly" props that go directly on to 3 mm shafts also have that phunky hex nut boss, but they vary in the depth of the boss. Therefore, some prop savers fit snug to the face of the boss and some of them smack the bottom of the boss, so the prop wobbles on the saver. Is this the kind of info we can collect?
I took the first few steps and setup a prop page that is similar to the motor pages. Its has the same graph as the thrustCalc, but also include additional information. This is just a rough first draft of the page and it will most likely change some, so if you have suggestions let me know. Which brings me to my next question, what exactly would everyone like to be include in the prop database?

A few that I can think of would be the hub diameter and thickness, and the diameter of the hole for the motor shaft.

Heres a link to the page for an APC SF 9x4.7

Now for a few fun facts
Dr Kiwi's favorite prop to test is a GWS HD 9x5 which he has done 1085 times. Followed closely by the GWS HD 8x4 in second place with 1036 tests. In third place is the GWS HD 10x6 with 887 tests.

Robert
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Old Feb 26, 2011, 10:43 AM
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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.
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Old Feb 26, 2011, 12:14 PM
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Hmm. Exactly what are the RPM limits for these props? We really need some numbers here, because the bulk of the prop manufacturers ain't talkin'. I realize that with the lightweight GWS props they howl and sing long before they become dangerous, but what about a nice APC or Master? And how do wood props compare to nylon or to thermoplastics?

Does anybody have a good feel for this? Should we be tickling the AMA to go after prop manufacturers to come up with better specs? You know, what with this new potential legislative challenge to aeromodeling the OEMs might want to produce these numbers to prove that they're safety conscious and doing their due diligence, yada yada.
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Old Feb 26, 2011, 12:33 PM
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Quote:
Originally Posted by Dr Kiwi View Post
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.
That makes sense too me. I just happened across one of the GWS HD props while I was testing and saw there were a ton of data points for it. That got my interest peaked so I did a quick check to see how many there were and found it interesting.

Robert
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Old Feb 26, 2011, 01:16 PM
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Originally Posted by A Useless Geek View Post
Hmm. Exactly what are the RPM limits for these props? We really need some numbers here, because the bulk of the prop manufacturers ain't talkin'. I realize that with the lightweight GWS props they howl and sing long before they become dangerous, but what about a nice APC or Master? And how do wood props compare to nylon or to thermoplastics?

Does anybody have a good feel for this? Should we be tickling the AMA to go after prop manufacturers to come up with better specs? You know, what with this new potential legislative challenge to aeromodeling the OEMs might want to produce these numbers to prove that they're safety conscious and doing their due diligence, yada yada.
As far as I can determine: APC (and, for some, Graupner) give RPM limits.

APC E = 190,000rpm/diameter
APC SF = 65,000rpm/diameter

Graupner SF = ~88,000rpm/diameter

My guesstimates:

GWS HD, around 100,000rpm/diameter

GWS RS, around 50,000rpm/diameter
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Old Feb 26, 2011, 02:54 PM
Jack
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Master Airscrew (aka Windsor Propeller Company) also publishes a limit, 165,000/prop Dia. in inches:

http://masterairscrew.com/images/selecting_a_prop.pdf

Jack
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