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Old May 13, 2010, 07:34 PM
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Originally Posted by HawkerTyphoon View Post
OK, here's one,

When giving you your prop selection what does the TE stand for, I get SF stands for Slow Flyer but I can't figure the TE out

Thanks,
HT
Excellent question, and I'm glad you asked it. All props have a safe rpm level that we never want to exceed, else they might disintegrate and throw shrapnel everywhere. This ain't good. Let's look at some props and see what the maximum safe rpm levels are. Thanks go to Dr Kiwi for providing the data.

APC TE(Thin Electric) or sometimes called APC E (Electric) have a safe operating rpm of 190,000 divided by the prop diameter. So an 8" diameter APC TE prop would have a max safe speed of 190,000/8 = 23,750

And APC TE 10" prop would have a max speed of 190,000/10 = 19,000 rpm. And so on and so forth.

APC SF (Slo-Flyer) props have a safe rpm of 65,000/diam. So an 8" SF prop would be safely maxed out at 65,000/8 = 8125 rpm, and an APC 10" diameter SF prop would be 65,000/10 = 6500 rpm.

A typical GWS RS (Reduction Series) prop has a safe rpm of between 40,000/diam, and 50,000/diam.

It is interesting to note that you might be playing with WebOCalc one day, working on dialing in a prop, and all of a sudden the prop disappears from the chart! The reason is because WOC will not let you choose a prop that is unsafe for the plane. So if in the process of dialing the prop in, WOC sees the rpm going up to the danger level for that particular prop, it simply removes the prop from the chart...

Chuck
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Old May 13, 2010, 08:22 PM
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Cool thanks!

HT
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Old May 14, 2010, 03:12 PM
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Here's another question,

when it gives you your amps, is that at full throttle?

HT
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Old May 14, 2010, 04:34 PM
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Here's another question,

when it gives you your amps, is that at full throttle?

HT
Yep, the current (amps) displayed is at Wide Open Throttle.
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Old May 15, 2010, 10:51 AM
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Good work on this Chuck. I followed the link from my question on using the plane weight when picking a motor. The first thing WOC asks for is the ready to fly weight of the plane. Is the weight of the motor included in the weight or is this the bare airframe weight? I guess my confusion lies in the fact that the tool helps you pick a motor, so if you haven't picked one how do you know how much it weighs.

I have a scratch build plane that weighs in at 12.5oz. bare and jumps to 20.5oz. when I add the weight of servos, battery, ESC and motor. I used an average for motor weight from an AXI catalog picking a motor that matched the size class of my plane. Should I use the weight of my plane minus the power train?
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Old May 15, 2010, 01:37 PM
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I have a scratch build plane that weighs in at 12.5oz. bare and jumps to 20.5oz. when I add the weight of servos, battery, ESC and motor. I used an average for motor weight from an AXI catalog picking a motor that matched the size class of my plane. Should I use the weight of my plane minus the power train?
Hi bullseye,

You should always use the weight of your plane as it sits on the runway, battery installed, and ready to take off; what we call the All Up Weight (AUW) weight.

And yep, it seems kind of funny that in order to pick the right motor, we are asked to use the weight of the unknown motor in our calculations...

But you found an excellent way of getting past that in your 'average weight' of motors in that size range! So that once you run the first calculation, and find out what WOC recommends for a kV value and current draw, you can go back to the catalog and pick the exact motor you need, and get it's exact weight. That's good thinking on your part!

Chuck
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Old May 15, 2010, 05:13 PM
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Good enough I'm on my way.
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Old May 15, 2010, 05:43 PM
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For those of you who are following along and want to try your hand at a good practice exercise... See what WebOCalc recommends I use on myParkZone Slo-V for "Gentle Scale Flying".

AUW = 16 ounces
Wing Span = 48"
Wing Area = 575 inē
Largest prop that will fit on my plane is about 12" in diameter.
I want to fly it in a "Gentle scale flight" manner.

Get WebOCalc here.
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Old May 15, 2010, 08:40 PM
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How about a GWS RS 11X8 on a 600 KV motor pulling 5 amps on a 250Mah 2 cell bat.

HT
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Old May 15, 2010, 09:10 PM
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Yesssssssssssss

25 mph, 14 ounces of thrust, on only 5 amps of current!

So I look in my box of motors, but the closest thing I have to that is a 920 kV motor.

So what battery and prop should I use for my "Gentle Scale flight"?
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Old May 16, 2010, 01:27 PM
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APC TE 10X5 920 KV 5.7 amps 350mah 2Cell

HT
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Old May 16, 2010, 01:48 PM
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Looks like you don't need me anymore... GREAT JOB!!!

24 mph, 11 ounces of thrust.
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Old May 16, 2010, 05:19 PM
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Hahaha, thanks, I love "easy" challenges like that,

HT
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Old May 17, 2010, 05:05 PM
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Hi Chuck,Excellent thread and probably the most valuable one I have found on RCG so far. I just wish I had found it earlier as I have smoked several motors and escs and been frustrated with the trial and error method of matching.
My flight style is FPV motorgliders. I typically use folding props, so diameter isnt usually an issue other than at low airspeed, large props droop a bit when folded. Any tips about using the calculations for folding props?
Thanks for the excellent "Dummies Guide"
Cheers
Frank
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Old May 17, 2010, 06:15 PM
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This is perfect! You've made everything so simple! thankyou very much
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