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Mister Softee
03-16-2007, 02:39 PM
I have a 14 x 7 prop and would like to use a smaller dia. because it hits the ground. What pitch should I use if I want a 11 x ?

Thanks in advance...

slipstick
03-16-2007, 04:03 PM
Changes in diameter have a lot more effect than pitch changes and that's a very big change....for equivalent POWER you'd need something like 11 x 15 or a 3-blade 11 x 12 (which don't exist and probably wouldn't work at all well anyway).

Going to an 11" prop will lose you a lot of thrust unless you also increase the voltage to get more rpms. Ideally if you want to use a much smaller prop you need a different motor.

Steve

CitaFly
03-16-2007, 04:59 PM
A 14x7 GWS RS will generate 984 grams thrust @ 4020 rpm.

An 11x7 APC E will generate 978 grams thrust @ 6800 rpm.

What will work for you depends on the specifics of your setup - battery, ESC and motor. Just changing to a lower sized prop, as Steve indicated, will change the rpms you need for equivalent power and could lead to a meltdown.

skiman762
03-16-2007, 05:09 PM
A 14x7 GWS RS will generate 984 grams thrust @ 4020 rpm.

An 11x7 APC E will generate 978 grams thrust @ 6800 rpm.

What will work for you depends on the specifics of your setup - battery, ESC and motor. Just changing to a lower sized prop, as Steve indicated, will change the rpms you need for equivalent power and could lead to a meltdown.


Be careful when comparing thrust like that even though the apc numbers look good thrust will fall off much faster then the larger prop as the rpm is reduced because the pitch speed will drop faster on the 11 then it will on the 14 not a big problem if you fly close to WOT but a killer on a 3d ship or casual flyer
Just my 2 cents learned the hard way

GA-Flyer
03-16-2007, 06:11 PM
I was following this thread and it seems like a great thing to have would be a chart that has prop size and arms as the x-axis and rpm as the y axis and the intersection being thrust. Does such a thing exist, sounds like an awesome cheat sheet for this hobby.

Doyle

CitaFly
03-16-2007, 06:39 PM
How about this? This is from my article on HobbyZone's Brushed 480 based on tests I did:

http://www.ampaviators.com/index.php?option=com_content&task=view&id=39&Itemid=28

Skiman is right on - the 10x6 curve shows you have to keep rpms up to hit equivalent thrust levels compared to the others - the flying will definitely be different.

skiman762
03-16-2007, 06:45 PM
It just adds to the endlest choices in power systems
guess that's why I have so many props sitting around but there cheap enough so if I get close on motor choice I can find a prop that works well if not I buy another motor and tell the wife I need a new plane for the old one:D
so it's win win for me

Mister Softee
03-16-2007, 09:12 PM
I have some more info for everyone to mull over. Here is the engine link http://www.hobby-lobby.com/brushless-axi2826.htm and if you scroll below it says ...:

3 lipos -14 x 7
4 lipos - 11 x 8
5 lipos - 11 x 6

What I want to do is run an 11 inch prop with 3 cells (11.1)

Thanks to everyone for their input...

Eric
I have a 14 x 7 prop and would like to use a smaller dia. because it hits the ground. What pitch should I use if I want a 11 x ?

Thanks in advance...

skiman762
03-16-2007, 09:42 PM
You will not be happy with the results
how much ground clearance are you looking for maybe larger lightweight wheels or taller landing gear would help

CitaFly
03-17-2007, 03:30 PM
This link gives more prop choices:

http://www.modelmotors.cz/index.php?page=61&product=2826&serie=10&line=GOLD

With 3 cells, I think you'll be running wot a lot.