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Jan 12, 2015, 04:18 PM
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Hi Louis,

Can you tell us more about Murat Vural formula ?

F =rho Kt (D/P)^0.7 P D^3 n^2

What are the units ?

Who is Murat Vural ?

C'est le grand Duduche qui demande
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Jan 13, 2015, 05:40 AM
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Fourdan's Avatar
Thread OP
Quote:
Originally Posted by yomgui
Hi Louis,

Can you tell us more about Murat Vural formula ?

F =rho Kt (D/P)^0.7 P D^3 n^2

What are the units ?

Who is Murat Vural ?

C'est le grand Duduche qui demande
Hi
Some months ago, Murat VURAL
Associate Professor of Mechanical and Aerospace Engineering
Illinois Institute of Technology
MMAE Department
responded to my question. He wrote :
"For simplicity, I take F in [lb], D & P in [in], rho in [lb/in^3] so that Kt comes out as about 0.05"
"Please note that this is a semi-empirical relationship with quite some simplifying assumptions. However it gives pretty good results once calibrated with experimental data"
....
The choice of units is governing the right coefficient Kt
Personnally in Scorpion Calc (SC) I have my own formulaes with Kp and Kt around "1" (default values).
My task of improving SC is not finished.
I am disturbed by the temporary absence of APC data on the APC website
Louis
Last edited by Fourdan; Jan 13, 2015 at 08:04 AM.
Jan 13, 2015, 06:27 AM
If it has wings it will fly...
ckleanth's Avatar
last year I have made a copy the apc data, do you want to upload them here or am I going to get in trouble with apc? why did they remove them data?
Jan 13, 2015, 08:03 AM
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Fourdan's Avatar
Thread OP
Hi
Thanks Ckleanth
I was in contact (by email) with APC beginning of december 2014
They suggested to me, to wait for "january 2015"
I am ready to message them around 1 feb 2015
Louis
Jan 13, 2015, 05:55 PM
If it has wings it will fly...
ckleanth's Avatar
well here is all my downloaded APC props data
Jan 14, 2015, 03:54 PM
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Thanks Louis !

I'm curious to see the new APC data.

The old data were very strange, far away from all the wind tunnel data I've seen. I don't know how APC got there data, but surely not wind tunnel, nor BEMT (blade element momentum theory).
Jan 21, 2015, 05:42 PM
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Fourdan's Avatar
Thread OP
Hi
APC website is back again (regarding performances data files)
I didn't check if data are new or different (/2014)
Louis
Jan 22, 2015, 02:26 PM
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Checking it !

Looks far better !
Jan 22, 2015, 07:25 PM
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Ok,

I've just wrote an article about it here :

http://aerotrash.over-blog.com/2015/...hat-s-new.html

They really made an effort, that's very good. But vortex theory has its limits, especially for small propellers...

They can't test all their props in a wind tunnel, that would cost a lot.

So, not perfect, but really a good idea.

APC props are my favorite propellers !
Jan 23, 2015, 04:12 AM
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Fourdan's Avatar
Thread OP
Hi Guillaume
Very good article on your blog.
You could just precise the units for thrust and power (I suppose kgf and W)
Best
Louis
Jan 23, 2015, 03:57 PM
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Hi Louis,
Thrust in N,
Power in W,

I corrected Ct and Cp formula (I forgot thrust and power in it... it was a bit useless )

A+
Jan 27, 2015, 08:48 AM
Registered User
Ken Myers's Avatar

APC data help please


I can't figure out what the PWR (HP) is referring to in the APC data. The image is from the APC 12x8E data.

A little help would be much appreciated.
Jan 27, 2015, 10:46 AM
Jack
jackerbes's Avatar
I have found the data in the first line of each 1000 RPM increment of the APC testing data to be useful and to compare well to my static testing results and the static testing results at flybrushless.com.

If you look at the APC Thin Electric 12 x 8 data here:

http://www.apcprop.com/v/downloads/P...PER3_12x8E.dat

I would use the wonderful and free Josh Madison Convert for Windows application to do all of my Imperial to Metric (and others too for that matter) conversions:

http://joshmadison.com/convert-for-windows/

I would use Convert to convert the PWR (Hp) values in the first line of the 9000 RPM data bliock you have posted above as follows:

Input Power = 1 HP = 749.6W = 1.082 HP x 749.6W = 811W

Thrust = 1 Lbf = 453.6 gram force = 5.781 Lbf x 453.6g = 2622 g

There has been a very limited amount of prop testing data posted to flybrushless.com on the APC TE 12 x 8 but there is some. If you look at the flybrushless.com Thrust Calculator here:

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

The flybrushless.com Thrust Calculator calculates a 9000 RPM thrust of 2477g for the APC TE prop.

There is not input power calculator at flybrushless.com but I look at the listing of test results for the APC E 12 X 6 prop here:

http://www.flybrushless.com/prop/view/53

I can draw some simple conclusions about the input power the prop needs at a given RPM. The Bruce Abbott data shows a test result as follows:

Input Power = 396W
RPM = 7251
Thrust = 1498g

Some of the other test data shows the prop as needing around 300W or so of power to get to the 7000 RPM level.

The APC data for 7000 RPM, with the values converted as above, shows a input power of 216W and a thrust of 1532g. So I would consider that, in at least that case, the APC input power numbers are not useful but the thrust value is.

So, for my simple needs, I have determined that I can take the APC data and convert it as I did above to get a rough idea as to the input power (in some cases) and thrust (in most or nearly all cases) for a given APC prop at a given RPM.

Jack
Jan 27, 2015, 12:39 PM
Registered User
Ken Myers's Avatar
Thanks Jack.

I've read and reread your post very carefully. In an obtuse way I believe you are saying the APC HP (horsepower) indication is power in.

My question, Power into what?

That makes no sense to me. Power out is totally relative to what is doing the power conversion from power in.

I assumed, and it appears incorrectly, that the HP (horsepower) indication was shaft horsepower, the power required to turn the prop at a given RPM.

Of course it can all be changed to watts for our use.

Using APC's data for the n100W number for the 12x8E, 5281 yields;
9000 RPM / 5281 = 1.7042227 ^ 3 = 4.9497017 * 100 = 494.97017 watts OUT, or absorbed by that 12x8E turning 9000 RPM or about 0.66 SHP (shaft horsepower)
75% efficiency yields 660 watts in
80% efficiency yields 619 watts in
85% efficiency yields 582 watts in

At 7000 RPM
7000 RPM / 5281 = 1.3255065 ^ 3 = 2.328872 * 100 = 232.8872 watts OUT, or absorbed by that 12x8E turning 7000 RPM or about 0.31 SHP (shaft horsepower)

I really appreciate your input, but I'm still confused as to what horsepower APC is referring to.
Jan 27, 2015, 03:02 PM
I am a nice guy! Really!
The "power in" in the case of the APC Charts is "power in" to the prop itself. It is the actual power required to turn the prop, not the power into the motor or whatever is turning the prop.


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