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Old Oct 09, 2012, 10:27 PM
Registered User
United States, MI, Waterford Township
Joined Aug 2012
53 Posts
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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, 11:32 AM
Damn this gets addictive.
Thechittyfather's Avatar
United Kingdom
Joined Oct 2011
515 Posts
Pretty much everything you need to know here.
http://www.rcgroups.com/forums/showthread.php?t=1136470
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Old Oct 10, 2012, 05:36 PM
Young Poor and Fun
United States, TX, Austin
Joined Sep 2012
101 Posts
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!
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Old Oct 10, 2012, 09:17 PM
Registered User
United States, MI, Waterford Township
Joined Aug 2012
53 Posts
Thanks for the tips. I'm just noew learning myself but I'm having a blast in the process.
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Old Oct 10, 2012, 10:35 PM
I ask a lot of questions.
Canada, AB, Airdrie
Joined Aug 2012
160 Posts
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?
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Old Oct 11, 2012, 01:16 AM
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LawnDartMike's Avatar
United States, OR, Salem
Joined Jan 2012
287 Posts
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.
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Old Oct 11, 2012, 02:57 AM
Damn this gets addictive.
Thechittyfather's Avatar
United Kingdom
Joined Oct 2011
515 Posts
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.
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Old Oct 11, 2012, 07:56 AM
SG Talon... Super Genius.
Lenox, Michigan
Joined Nov 2005
3,135 Posts
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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