10x8 4 blades

[realbob]

Hi, anybody tried running with a 4blade prop?

I am new to this so I don'T really know advantage would it have to have 4blades vs 2 Any idea?

[flydiver]

On the stock motor with 3S? > major meltdown.

Weird as it may sound 4 blades are not as good as 2 blades. The reason you add more blades is if the plane design cannot add more blade length which would be more efficient. So you add blades if you need the thrust but can't deal with the length, usually ground clearance.

Looks cool though......

[realbob]

Thanks!

But if the plane can use a 10x8 2blades, why a 10x8 4blades would not have clearance? 10 means 10 inches am I right?
WOuld it be heavier so I could burn out motor faster?

[flydiver]

You have clearance, that's not the issue. Clearance was a general statement for any plane using multi-blade props.

Each blade provides thrust. Each blade consumes power. Each blade adds to turbulence and drag.
The OLD NIMH powered Cub (meaning lower voltage and lower power) used the 10x8 prop. As voltage goes up, RPM goes up and power goes up, but the motor has to pay for this. The electronics of the Cub have NOT been upgraded to deal with this so the prop was made smaller (9x6) to prevent electronics failure. The 10x8 is used by the float planes for short bursts of power. Continuous use is highly likely to burn something up.
Add 2 more blades to that and you increase power draw and you increase prop turbulence. Yes, you will increase power output, but only until something fries. It'll be short lived glory. It's kind of like putting a 12x8 or so on it-way too big.

Analogy-you can't pull a 50' trailer with a Volkswagen bug without consequences. You got to get a bigger motor. You can't increase the power output of a given motor beyond it's limits. The stock Cub is at it's limits.

There's kind of a rule of thumb for this-for each blade added you may need to subtract an inch of blade. With the wide variation in blade styles, and the issue of pitch the only sure way to tell is with a wattmeter, a device for measuring power output and battery draw.

Take a look at these to get a better handle on it:
www.zingerpropeller.com/_2_blade_.htm
www.mh-aerotools.de/airfoils/propuls2.htm

[realbob]

Thanks! This was very usefull! So I guess I will stick with stock prop for now! I just wanted to have a neat mod that nobody has or almost nobody has and is not too complicated to do!!!

[flydiver]

You could try this.
www.headsuprc.com/servlet/the-1547/GWS-8040x3-Standard-Rotation/Detail
Probably won't do any harm, may not do any real good.

If you think a prop mod is easy you haven't swapped out too many props. The things drive me crazy. There are no real standards and nothing ever seems to fit anything without messing around with reamers and shims.

[realbob]

Ho boy, another universe of non standard I guess!!! I am used to this!

I used one of your reference and if I am calculating the good way with their formula, I would need a 8x6 3-blades and it would fit perfectly.

Will see if I take chances in burning motor or other stuff! Will keep posted if I do anything on that side!

Thanks for all the help!

[kenninny]

I flew my first cub the red one with lipo's without changing the prop, still kept the 10x8 prop on to see what would happen. the clear covers on the motor connector started to turn brown. and melt, could have fried the esc & motor, but I stoped just in time

[realbob]

Wow, this is amazing how a so "small" difference this can hurt the hardware!

So this means that if you fly with the floats on, you will burn something down??? This is quite weird of them!
I was planning in using the floats a lot..

I guess a motor upgrade could resolve thise issue....

[flydiver]

Floats create a LOT of drag, especially on take-off. The 10x8 does provide some extra power but at the expense of loss of efficiency and a lot of extra heat. So, you can only use it full throttle for short bursts.
Overloaded electrics create heat. ANY electric part getting so hot you can't hold it in your hand is too hot. If that happens even briefly to a lipo you are well on your way to ruining that battery.

9x6 > 10x8 in the electric world is not a small difference, it's pretty big.
An 8x4.3 slow fly prop (fat blade) is WAY bigger than an 8x4 direct drive (skinny blade). It probably pulls 50% more power.

You will notice a GWS 10x6 direct drive (skinny) being frequently suggested as a replacement for the 9x6 stock lipo cub prop (fat blade). They seem like completely different sizes but if the output is measured they are almost the same.

This is pretty normal in electrics. You'll find things rated at 'something' continuous and 'something' max for say 30 seconds. For Cheap Chinese parts (most of them) even that is pretty much a fiction and should be de-rated at least 20% if you don't want to run the ragged edge.

[realbob]

About heat, anybody tried adding a small fan inside the battery compartment to help cool down during flight? A low consumption fan that would barely shortens the battery file or could even plug on a 9v battery (more weight, taht I know!!!) But if it helps cool down specially with the floats on, would be any good idea?

[flydiver]

The holes in the battery box, cowl, and those exit holes on the bottom of the fuse are adequate cooling for the parts while flying.
More stuff like you suggest adds weight, which adds to the load, which adds to the heat to fly the extra weight. Result, debatable but likely a worse flying Cub due to weight gain that remains at about the same temperature.

Trying to cool electronics that are being pushed too hard by external means is somewhat counterproductive because it often indicates they are being run beyond their spec and not being as efficient anyway. As heat goes up, electrical resistance increases and efficiency goes down.

Lack of adequate cooling is why you shouldn't do extended motor runs with the plane secured and not moving.

The real problem with floats is wet electronics. There are special corrosion applications for that you need to check into.