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Old Oct 09, 2012, 11:27 PM
Tommy21781xxx is offline
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Discussion

Power to weight question


Hey everyone, I'm in the process of building a t-28 out of dollar tree foam. I'm using the VLM method. At this point I have all of the pieces cut out and with paper still on the foam and no glue, I'm at 126g. Say for example my bird weights in at 250g, how much pull should I look for in a motor.

I ask in terms of pull b/c I'm looking at a motor/esc combo from hobby parts and the motor I'm thinking of has 600g of pull. I'ts the dynam 18amp esc/motor combo.
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Old Oct 10, 2012, 12:32 PM
Thechittyfather is offline
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Damn this gets addictive.
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Pretty much everything you need to know here.
https://www.rcgroups.com/forums/show....php?t=1136470
Old Oct 10, 2012, 06:36 PM
Y.P.F. is offline
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Young Poor and Fun
Hi Tommy2178xxx,

I found this HK tutorial after learning more about motors, I wish I read i sooner: http://www.hobbyking.com/hobbyking/store/ebasic.asp.

600g thrust for a 250g airplane sounds way overpowered. I’ve read that anything with ~150% thrust to weight is a very respectable 3D flier. So you could get away with 375g of thrust if your goal was to make it really overpowered. Anything else is probably just gratuitous vertical acceleration Yee Haw!

My lady and I just set up a similar thrust-to-weight ratio on a slow stick and it's a blast. I’ve got a low KV motor with a large prop and at WOT it goes the same speed in any direction but it’s not very fast.

If you want to go fast, I’d recommend a higher KV setup. It’ll probably look more natural for a T-28 to scream around and have a more reasonably sized prop.

I don't know if you already know this stuff, I'm just learning it myself.


Sounds cool BTW, you should totaly post pics and video!
Old Oct 10, 2012, 10:17 PM
Tommy21781xxx is offline
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Thanks for the tips. I'm just noew learning myself but I'm having a blast in the process.
Old Oct 10, 2012, 11:35 PM
Disco Stew is offline
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I ask a lot of questions.
Sorry to hijack...but is there a good tutorial on understanding all the prop number?
i.e. 10x7.5SF....What do the letter designations mean?
Old Oct 11, 2012, 02:16 AM
LawnDartMike is offline
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The SF is for Slow Fly. They are props made to generate more thrust at low RPM for use on low KV motors. Mainly for 3D flying.
Old Oct 11, 2012, 03:57 AM
Thechittyfather is offline
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Damn this gets addictive.
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Letters after the prop size are supposed to be an indication of suitable use but what I've found is that prop choice ends up coming down to a. Which props will fit on your motor shaft/prop saver and then b. which one of those props gives figures within the appropriate tolerances on your watt meter.
Old Oct 11, 2012, 08:56 AM
SGTalon is offline
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SG Talon... Super Genius.
Less weight = better flying plane.

I always base my motor decision on thrust and weight. Lots of websites like www.headsuprc.com have detailed information on what kind of thrust and amps each prop size puts out. I always go with better than 1:1 thrust to weight and I am safe. But i really like to be in the 1.5 or 2:1 region.


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