I found the attached diagrams on the Aeronaut web pages and it has been helpful as far as estimating the power needed to get various folding props to a given RPM. I doubt that it is dead accurate but it is a starting point. Haven't found a similar chart for Graupner or other folding prop blades.

If it is not obvious, the two axis on the graphs are RPM x 1000 on the bottom and input power in Watts on the left.

The Europeans seem to favor using the N/100 spec in some prop specs. That is the rpm obtained with 100 watts of power driving the propeller. But to my non-European way of thinking the number does not mean much to me.

There are also some spreadsheets with translated names like "air screw comparative values" available on the Aeronaut download pages. Those can be run with OpenOffice Calc or Excel and have a lot of meaningful specs in them. I have not studied those at all, too many numbers and too much German that needs to be translated in the column headings.

Hyperion has a good discussion of some of the technical mysteries about props here:

http://aircraft-world.com/prod_datas...p-proptalk.htm

Jack

Do these graphs represent thrust somehow? Newtons or something?

"Leistung" = power
"Drehlzahl" = rpm

Try using Propeller Calc or PropCalc in combination with DriveCalc or Scorpion/Dualsky/MotrolFly/ Calc:
http://www.rcgroups.com/forums/showthread.php?t=606703

Vriendelijke groeten Ron
• diy motor tips • Drive Calculator •
• diy motor group • Cumulus MFC •
• Get a life ... get a Watt-meter!!! •

Originally Posted by A Useless Geek

Do these graphs represent thrust somehow? Newtons or something?

No, and that is what we are used to seeing in prop testing results done here.

I think the assumption is that you want to know how many Watts it take to get it up to a certain RPM. .

It might help if I understood the spreadsheets (in German) better. Here is the data that is in one of the spreadsheets in a *.pdf document:

The document is called a Klappluftschrauben Vergleichstabelle and that means "Folding air screw comparison table".

http://www.xxl-modellbau.de/abbildun...hswerte_01.pdf

But I could really use an explanation as to how to use the info there.

Jack

thanks for the info,but boy its complicated.
my setup at this time on my spider 2.5m is
Hyperion HP-z 3025-10
Hyperion 80a with cool BEC
15x10 aeronut
2x3s 2500 25c GEN ACE in par.
my watt meter shows 1090 watts @ 90 amp
i needed to find out if with changing prop i can keep the amp with about 1200 watts.
thanks
ben

Originally Posted by FASTBEN

thanks for the info,but boy its complicated.
my setup at this time on my spider 2.5m is
Hyperion HP-z 3025-10
Hyperion 80a with cool BEC
15x10 aeronut
2x3s 2500 25c GEN ACE in par.
my watt meter shows 1090 watts @ 90 amp
i needed to find out if with changing prop i can keep the amp with about 1200 watts.
thanks
ben

Your results are interesting. But I think something might be wrong with your setup. Do you have the batteries in series or in parallel?

You are getting a 90A load with an input of 1090 Watts. Do you happen to know the RPM?

The Aeronaut diagram for the 15 x 10 folder shows that prop using 650W at 6,500 RPM. And the Hyperion test data for your motor on 3S and with a similar sized, but slightly smaller and non-folding prop, as:

APC 15×8E
3 cells
10.05V
51.1A
514W
6270 RPM

I can't understand why you are getting current readings that high, but you are already well over the 65A Max Current rating for that motor and I would think it would be overheating now.

I have used a few folding props, none that large through, and have generally found them to draw similar amounts of current to what would be drawn by a similar sized fixed prop.

Jack

Here's some real-world test data for your motor: Bungymania Motors Data Base: Hyperion z3025-10

For working out what's best I use Motocalc, because it calculates the performance of the whole system (not just the motor). It costs $39, but is free to download and try out for 30 days. Here's a sample output:-

Motor: Hyperion HP-Z3025-10 (bungymania); 933rpm/V; 3A no-load; 0.05 Ohms.
Battery: Hyperion G3 CX 2500 (25C); 3 series x 2 parallel cells; 2300mAh @ 4.02V; 0.0021 Ohms/cell.
Speed Control: Hyperion Titan 80 BEC; 0.0012 Ohms; High rate.
Drive System: Aeronaut Folding 15x10; 15x10 (Pconst=1.11; Tconst=1) direct drive.
Airframe: Spyder 2.5m; 714sq.in; 70.1oz RTF; 14.1oz/sq.ft; Cd=0.036; Cl=0.42; Clopt=0.67; Clmax=1.04.
Stats: 242 W/lb in; 143 W/lb out; 19mph stall; 24mph opt @ 31% (92:00); 30mph level @ 38% (63:56); 2840ft/min @ 90°; -143ft/min @ -3.9°.
Conditions: Sea Level, 101.3kPa, 20°C

AirSpd (mph) = 0.0
Batt Amps = 90.8
Motor Amps = 90.8
Motor Volts = 11.7
Input (W) = 1059.3
Loss (W) = 433.7
MGbOut (W) = 625.6
MotGb Ef(%) = 59.1
Prop RPM = 6647
Thrust (oz) = 116.6
PSpd (mph) = 62.9
Prop Ef(%) = 0.000
Time (m:s) = 3:02
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This was done by one of the members on my setup.and yes the 2x2500 batts are in paralel.post#4.@ 8 to 10sec motor run.on on/off switch.
http://www.rcgroups.com/forums/showthread.php?t=1631341

Ben

I guess I don't get it then. Either the motor is very conservatively rated at it's 65A max or there is an error there maybe.

Does that 59.1% efficiency look typical to you? I sort of wonder if you couldn't get that prop up to the same or nearly the same RPM with less throttle, lower current, and see better efficiency too. I have seen similar things when I flew an eLogger and noticed that the last 20% or so of throttle movement and input power only made for a very small RPM increase (300 RPM or so). So the extra power went more to warming the air around the plane than making it fly any better.

Jack

i only use motor in 6 to 8 sec burst,in 20 to 30 min flight time maybe 18 to 20 sec motor run and it is eather on or off there is no throttle controll.
and yes that motor is under rated.
Ben

I've heard of 'Motor-Calc' but never looked into in any detail, hence my question.
The 'elementals', such as particular motor brands & models; ESCs; and possibly the same on LiPo's used -- are all these elements pre-loaded into the program's onboard database? Or can/must one 'load' the elements' performance figures or specs first in order for the program to calculate & 'do its thing'?

I'm sure Motor-Calc is a good product and worth it's price. There is another well thought of RC power calculator called Drive Calculator that is free for the download. It can be downloaded here:

http://www.drivecalc.de/

There is a companion program named Propeller Calculator available there too.

Jack

Originally Posted by StarHopper44

I've heard of 'Motor-Calc' but never looked into in any detail, hence my question.
The 'elementals', such as particular motor brands & models; ESCs; and possibly the same on LiPo's used -- are all these elements pre-loaded into the program's onboard database? Or can/must one 'load' the elements' performance figures or specs first in order for the program to calculate & 'do its thing'?

MotoCalc and DriveCalc both have large numbers of motors/props "pre-loaded"... so that all you need to do is select a motor and a prop... add in the voltage you wish to use... and the programs will compute the rest for you.... it is a great way to play with props and voltages to see what might work for you... rather than having to go out and buy motors and props.. and then find you made lousy choices.

You can also add your own test data if you wish.

Originally Posted by FASTBEN

and yes that motor is under rated.

Just because you're getting away with it, doesn't mean the motor is under-rated. You are running a duty cycle of around 1%. In other applications that need high burst power (eg. F5F hotliner glider, 3D aerobatic plane) the duty cycle might be 10% or higher. That would create 10 times greater temperature rise, and probably a cooked motor!

Maximum power transfer is achieved at 50% efficiency (which means that half the power is being wasted). That is how you get the absolute highest possible power output, but backing the loading off a bit won't reduce it by much. You could drop down to a 14x9 prop and get almost the same climb rate, but with less risk of burning up your ESC.

that is a great info,i will try the 14x9 also and see what i will get.
thanks
Ben

Here is the eLogger data plot on my "air warming" demo. The input power goes from 205W to 245W and the RPM only increases by about 300 RPM or so.

So that might be another case where dropping back to a 13 x 6.5 or so would find a middle ground in there with more RPM at a lower input power, and maybe even a plane that flies better.

Jack