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Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

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Old 02-24-2008, 05:28 AM   #1
diverdon
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Default Prop Crossover chart ??

Hello everyone , Please , Please can someone tell me if there is a chart or a formula to help pick prop sizes?? Like lets say you have a plane running with a 10 X 8 prop and you'd like to go with an 11 inch prop (just for instance) I am pretty sure you could do it if you toned down the pitch of the prop ..

Has anyone ever heard of any kind of a chart to help pick props this way ?? And as allways ... Thanks so much , Don J.
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Old 02-24-2008, 06:30 AM   #2
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Originally Posted by diverdon View Post
Hello everyone , Please , Please can someone tell me if there is a chart or a formula to help pick prop sizes?? Like lets say you have a plane running with a 10 X 8 prop and you'd like to go with an 11 inch prop (just for instance) I am pretty sure you could do it if you toned down the pitch of the prop ..

Has anyone ever heard of any kind of a chart to help pick props this way ?? And as allways ... Thanks so much , Don J.
Hi Don I dont think that there is such a thing, Because there are so many different types of props that have the same size but work different, for an Example an APC speed prop will not give you the same thrust as a APC thin prop or a SF prop, even though they are the same size, and will draw different amounts of current, Here is where you really need to get a Wattmeter, Now with your Example of a 10x8 prop, is it s Slow Flite prop SF , a thin prop , a speed prop, Etc, see what I mean, even though its a 10x8 prop ,there is a lot more info that needs to be given, the type of prop. SF, Speed, Thin etc., mfg of prop, weight of prop, Here is Something I do with a prop of the same MFG and TYPE, lets say a GWS SF prop
if I want to go up a size , lets say I Have a 10x8 , I will go 1" bigger Dia. and Drop 2 pitch sizes, so now you will have a 11x6 prop, that should be safe to use, but, Check it with a wattmeter to be on the safe side, another example with a GWS SF prop 7x6, I will go to a 8x4, up one 1" Dia.size, go down 2 on pitch, it seems to work well for me, but always double check Draw with a wattmeter, hope that helps, Chellie

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Old 02-24-2008, 07:11 AM   #3
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AHHH Ha!! --- Thanks Chellie , excellent answer I am tired that's my excuse and I'm sticking to it.. as to why I didn't think of it... .. I have heard of and looked at these Watt Meters for RC several times .. So Here's one of the reasons to have this..
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Old 02-24-2008, 08:39 AM   #4
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load is proportional to D^5*P (and rpm^3, but you would keep that constant). Your 10x8 would be 10*10*10*10*10*8=800000. The 11 inch prop would have to be 11x4.96 to give the same D^5*P. This works reasonably well for props of the same general design, like in looking for a new APC-E to replace another APC-E.

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Old 02-24-2008, 03:57 PM   #5
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What Chellie said. Hans gave you the 'formula'. Here's a chart if you stay in the same family of props. Goes into considerably more detail and is a good primer for props. Ultimately you want a Wattmeter to confirm the output.
http://www.ampaviators.com/index.php...d=66&Itemid=27

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Old 02-24-2008, 07:56 PM   #6
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that link gives 2 different formulas (D^3 and D^4).

Here is where the D^5 one in post #4 is from: http://www.mh-aerotools.de/airfoils/propuls1.htm (Martin Hepperle's site; follow the link to 'equivalent multiblade propellers' and 'optimum propellers').

Doesn't make much difference which one you use as long as the change in diameter is small. The 10x8 would be equivalent to a
10x6 with the D^3 formula
10x5.5 with D^4
10x5 with D^5
I believe the D^5 formula is in use for fullsize prop.

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