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Jan 06, 2015, 12:18 PM
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PAR Calculator


Here are some quick instructions for the PAR Calculator, which is still in beta. Some formatting changes and text corrections still need to be made, but I want to complete the beta testing so I can make all the semi-final changes at the same time.

I've also included an image illustrating the measurements that are required in order to calculate PAR values. These measurements should calculate to the exact same value as if we calculated the MAC (mean aerodynamic cord) and multiplied it by the wingspan. Anything close to a 100 PAR is very good, and you should find some that will be as high as 115.

Please remember that PAR is a highly subjective ranking, and you should instead focus more on the actual values associated with them, such as wing loading, wing cube loading, power loading (Watts per pound), pitch speed, stall speed, etc.

My suggestion is to add data for your favorite planes, and perhaps establish your own PAR. Then use the PAR Calculator to identify planes and power systems that share similar values with your personal PAR.

For more information about the PAR Calculator, PAR values, or to ask about a specific motor, prop, and cell count, configuration that you may be considering, feel free to ask.
Last edited by Aeroplayin; Oct 31, 2015 at 10:59 AM.
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Jan 10, 2015, 12:47 PM
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The beta for the PAR Calculator is over so you can feel free to use it here:

http://rcwebclub.com/rcwebclub/PAR.aspx
Feb 17, 2015, 11:56 PM
Yin & Yang
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Sub'd
Feb 18, 2015, 09:25 AM
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The are a few things I'm hoping to accomplish here.

One important topic is to make sure everyone has confidence in the way they are using it.

It is also important to get a better understanding for the way the performance values translate into what we feel in the air.

Once we gain confidence in what we are plugging into the system, and what it is telling us, the next thing to do is to get a feel for how prop size and material, along with the cell counts that are now available to us, can manipulate power, weight, and flight time, in a way that benefits us.

And, anything else that may come along when questions are raised. I'm much too close to the programming and process to see the full scope of what others see when they use the app, so feel free to ask questions, or for confirmation about the systems perceived value. With any application like this, the instructional documents are probably the biggest under-performer, so questions will help reconstruct a better How-To.
Feb 18, 2015, 03:45 PM
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what accounts for the difference in measured and calculated thrust?
Feb 18, 2015, 04:16 PM
If it has wings it will fly...
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combined motor & prop efficiency
Feb 18, 2015, 05:08 PM
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Quote:
Originally Posted by mattnat
what accounts for the difference in measured and calculated thrust?
Measured thrust is a value representing the physical thrust you would measure with a scale. It is still calculated, but will fall in line in a relative way when compared to a scale reading.

Calculated Static Thrust is the product of a formula that does not consider the propeller pitch. Although it doesn't seem like it, there's a very good reason for it.

In full scale planes, thrust in a static position is virtually meaningless. Static Thrust is calculated as a base value that when the airspeed is added, thrust at speed can be calculated. This is why pitch is not needed.

I like to represent measured thrust so that we can get a relative comparison in how different power setups "pull". That tug we feel will translate to how quickly a plane will recover from 3D maneuvers that end in a virtual stall (static) position. It will not translate to airpseed, or thrust at airspeed.

Pitch speed is useful only to provide an apples-to-apples comparison between the potential advance ratio of two different setups.
Feb 18, 2015, 05:18 PM
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Also... Static Thrust (Kg) is used in the formula for Propeller Absorbed Power along with (KPH).
Mar 03, 2015, 02:15 AM
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So Measured Thrust would be a better indicator of how hard it would pull out from a dead still hover, correct?
Mar 03, 2015, 02:17 AM
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One suggestion: Provide a way to export your results to a file, or a copy button to copy all of the input and output values and field names. I tried selecting everything, copying and pasting into Excel, but the prop diameter and pitch values did not paste over for some reason.
Mar 03, 2015, 09:04 AM
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Quote:
Originally Posted by Neil_SC
So Measured Thrust would be a better indicator of how hard it would pull out from a dead still hover, correct?
Yes.

Quote:
Originally Posted by Neil_SC
One suggestion: Provide a way to export your results to a file, or a copy button to copy all of the input and output values and field names. I tried selecting everything, copying and pasting into Excel, but the prop diameter and pitch values did not paste over for some reason.
Good idea. Every system we make exports data to Excel anyway, so it's not a hard thing to do. Finding the time is the only issue around here, but I will seriously look into that and see how long it would take. Thanks.
Mar 15, 2015, 08:05 AM
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could we get a motor class for 130-180g motors?

matt
Mar 15, 2015, 10:36 AM
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Quote:
Originally Posted by mattnat
could we get a motor class for 130-180g motors?

matt
I've had many motors from 150 to 280 grams, and the Motor Load Efficiency selection of "Less than 380 grams to 2000 Watts" will fairly consistently match the actual measured results.

For example, my 152g DM2820-680 will do 8100 RPMs, 680W and 47 to 48 Amps at 3.65v per cell with an APC 14x7. The performance was relatively excellent so the high PAR makes sense too.

But motors in the 65 to 110 range could used their own category, and is something I may add in the next update. Are there others that would benefit from smaller motor potentials from this tool?
Mar 16, 2015, 11:24 AM
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I got a PM question last night and I think it raises a good point about the Motor Load Efficiency selection. The really good motors we have tested will typically run at 4.0, 4.5, 5.0, and 5.5 Watts per gram with an acceptable load during bursts to WOT. You have to use this as a rule of thumb because there are too many variables involved to make this a truly usable constant.

3D airplane motors may weigh a little more considering the third large concentric bearing. We see this all the time with Motrolfly and Hacker, although Motrolfly still seems to come in lighter and run cooler, than most motors that can manage the 3D load.

The large concentric bearing is added to manage the forces that are produced when the torque vector chases the angular momentum vector in large diameter props spinning to higher RPMs with high acceleration inputs. A high-speed knife-edge spin with a large prop is generally the test for motors like this.

As motors get bigger and heavier, the efficiency will typically increase. So a 950g motor will spin a 22x10 prop faster on the same volts than a 700g motor, for example.

So for now, if you are running smaller motors under 130g, you can use this rule of thumb to confirm the PAR Calc output, and 4.0 W/gram is probably the correct value. Otherwise, the results that the PAR Calc displays are going to be as accurate as I have seen on any tool deployed for this purpose.

Here are some actual recent results collected under the same test conditions from 2500 to 5500 Watts motors with 20 to 24 inch props. All motors were run for no fewer than 10 seconds at WOT and the averages were taken from no sooner than the 3 second mark, and no later than the 10 second mark. So this is NOT results calculated from peak data.

Data was taken from an HV120 Ice2 ESC log on the version 3.27 firmware with fully charged batteries that were run for a few seconds prior to testing. Thrust measurements were also taken during the same time frame as the data was collected.

URPM/v is the RPMs per volt measured without the prop prior to testing on the cell count used for the test. Volts/S is the average volts per cell recorded for the test sample.
Mar 16, 2015, 11:36 AM
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Fourdan's Avatar
Hi Aeroplayin
Thanks for the file "Test Stand ..."
I would appreciate the info regarding the units for HP, torque and thrust
Louis


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