Prop options for a park 450
 

I'm converting my Hobbyzone Super Cub and putting in a Turnegy Park 450. The recommended prop sizes for this motor are 9 x 5 and 8x 4.3. Just wondering, can I try any other sizes with out causing serious damage to the motor? Like, if I wanted to get more torque, could I use a larger prop with a lesser angle... like a 10 x 4.7? Or if I wanted more speed could I use a 8 x 6? I'm not clear if you can mathematically stray from the recommended props for EP motors at all.

You certainly can try other options. Once you leave the security of RTF systems though it's very wise to get a wattmeter, learn how to use it, then you get proper answers to your questions.

Too small a prop > lacks power (may be more efficient though)
Too large > maybe burn something up.
Over propping is very common. Folks think they are getting more for nothing. Pretty much they are producing heat, running their batteries down faster, and feeling good about it.

So, there's a range that will work well. You need to stay inside that range and from there pick a prop that you feel works best for the plane and you.

Hi toonamelt, WELCOME to WattFlyer! It's always good to see new faces.

+1 to what flydiver posted.

A Wattmeter is a device that plugs into your setup in between the battery pack and the ESC. It then measures the Watts being generated, Amperage being pulled and some can measure mAh used.

I use mine every time I set up a plane. Even my BNF planes get measured so I know the base numbers.

Thanks flydiver and max2112. I recently got a watts up meter, and am just starting to get familiar with it. it's fun in a geeky kind of way. :)

So as long as the prop doesn't cause the motor (one ESC) draw more amps or watts than specked, than I should be fine? Sounds like I will just need to tests a few props then. Is there a formula for determining the efficiency?

To determine efficiency you need a few more tools (tachometer, IR thermometer, maybe even a thrust stand). Some folks go there but for most simply staying within the max spec range is suitable.
Generally you'd like to prop so max RPM is ~70% of max unloaded RPM. The motor should only get warm, not hot.
As there is poor cooling on the bench limit motor runs to less than 30 seconds. If a motor gets hot in that time > it's over propped most likely.

Beware of GWS SF props under much power. They are pretty floppy, distort readily (you can hear it) and if pushed can break. All props have a max RPM with the SF (skinny hub, fat blade) being lower than the thin electric (fat hub, skinny blade). APC publicizes that info, GWS does not.

Thanks again flydiver! You've been very helpfull!