10x 7 Prop Stock Super Cub w/ Floats???

[jimd0586]

Hey all,

I have a slightly modified Super Cub: Monokote over the wing and added ailerons. Everything else is stock. I have the float kit for my lake cabin but read the instructions and the forums online that say that the stock super cub motor will not handle the 10x8 prop for long before burning up.

I am not trying to get into a big discussion on the theory of props here, but if the 10x8 is needed to generate lift (I use the term lift generally) to get the plane and floats into the air over the stock 9x6, and the 10x8 is too much prop for the stock cub, could a 10x7 prop be used instead and maybe not burn up the engine? Or maybe a 10x6?

My general knowledge of props is that diameter equals thrust (acceleration) and pitch works on speed. My guess is with floats on I need thrust as the large wing creates a lot of lift at even low speeds, so the diameter would be more important than the pitch... is that correct?

Anyway, any suggestions on props to be used with the floats to limit the chances of burning up my engine would be greatly appreciated. Thanks all!


Jim

P.S. I can also post photos of my cub if anyone wants to see it. It's nothing amazing by any means. The monokote has plenty of wrinkles in it. As a law student I can't dedicate a ton of time to this thing!!!!

[kenninny]

The original red cub used the 8x10 prop with no problem, but it used a nimh battery witch is 9 volts,
now the cub use a lipo battery witch is 11.1 volts that makes the motor spin faster, and draws more
amps more volts = more power that's why the prop was downsized,changing the pitch will slow the plane,
but with the bigger diameter the motor works harder, and draw more amps, and also puts a strain on
the esc too.

[kenninny]

I forgot to say that the bigger prop is to help lift off the water, water creates more drag when your
in the air throttle back

[Knackered Sailor]

The amount of knowledge on this site never ceases to amaze me.

[flydiver]

The motor is not in any particular danger, the ESC is. The Motor is $10. The ESC+RX is $50. Funny how everyone gets fixated on the motor. The weak link is the ESC.
Read this. Keep reading it until you understand it.

Stock motor/prop/thread - Lets get it straight
supercubclub.proboards.com/thread/4624

People also think diameter and pitch are the determinants. Prop SURFACE AREA is the determinant. You generally do get that with length, but some props are FAT (slow fly type) and some are skinny (thin electric).
You can have a short FAT prop that draws more than a longer skinny one.
The 10x8 is both long and fat.
The lipo stock prop (9x6) as almost identical draw to a GWS 10x6 (thin) or an APCe 10x5 (thin electric). So, one of those props my help protect the power package but won't give you as much thrust.

The ONLY way to know for SURE what the draw on a 10x7 you want to try is to hook that up to a wattmeter and test it. There are simply too many 10x7 props. They simply will not all be the same.

You simply cannot get away with [not trying to get into a big discussion on the theory of props here] when you start throwing props at power systems. Props DEFINE the load and are critical.

[jimd0586]

Thanks for the replies guys. Flydiver, I see you on here talking about this a lot. Hopefully I'm not beating a dead horse here.

I'm also trying to understand this prop deal. How is a 10x7 less thrust than a 9x6? I figured it would be a little more as both diameter and pitch are higher...

[flydiver]

Apr 17, 2014 16:33:22 GMT 1 jimd0586 said:

Thanks for the replies guys. Flydiver, I see you on here talking about this a lot. Hopefully I'm not beating a dead horse here.

I'm also trying to understand this prop deal. How is a 10x7 less thrust than a 9x6? I figured it would be a little more as both diameter and pitch are higher...

The majority of questions in RC are beating a dead horse. Pretty much anything you can think to ask has been asked dozens if not hundreds of times. The problems are:
1. Being able to find it.
2. Being willing to look.

You cannot easily compare different brands and different styles of props.

It's all (well, mostly) about > Surface area....surface area...surface area

Imagine a really FAT 6" prop vs. spinning something the size of spaghetti but 12" long.
Which would be harder to spin?
Pitch is not as much of a variable as length and width > surface area, get it?

Here's a bit more info:
rc.markclarkson.com/?p=1719

Then take a look at this somewhat random motor choice (decent for a Cub upgrade) and the different amp draw as voltage (2S and 3S) changes with different props.
www.flybrushless.com/motor/view/199
Huge differences.

The GWS 10x6 pulls a lot less than the Horizon 10x8 even though they are the same diameter.

[jimd0586]

Thanks for all the info!

[flysc]

I've read much usefull information on this site regarding the 10x8 prop when useing floats on the stock Super Cub on this site. But I haven't read anyone trying the stock 9 x 6 on floats. My question is will the Cub fly? does it lift off the water?

regards
flysc

[sham]

The reason you use the larger prop on floats is to give it the extra shove it needs to break clear of the surface tension of the water.

I'd be surprised if it stopped it lifting off at all, but its going to take a lot longer to get the speed needed to gain enough lift - and if the water were anything other than perfectly smooth, the longer it takes to gain speed the more risk of a subcub.

[flydiver]

People used to use the old 10x8 with NiMh on floats. Jeez, somehow it worked in spite of more weight, less power.
With lipo and a 9x6 you have MORE power than the old system. It'll work.
Yes, you can put the old 8x10 (for floats) prop on, pull a LOT more power, get off the water even faster, but you risk frying that $50 ESC if you push it too hard.

[hghost]

My Stock Cub takes off in less than 8 feet......I would assume ( as i do not know and do not fly off water) BUT it would take
at least double that length to get off the water , say 16 feet or less ?