Prop for Stock Motor, Aftermarket Electronics

[flydiver]

I just re-read your question.
I answered it.
There are links to actual tests with different props and different voltages.
You want more data, get a wattmeter, test stand, tachometer, infrared thermometer, a bunch of props and have at it.

But let me repeat - HZ provides NO DATA AT ALL ON THESE PRODUCTS. It "appears" it is a 13A motor and maybe a 15A max ESC (maybe....on a good day, with cool temps and good ventilation). Those are lines in the shifting sand of HZ non-disclosure. Cross 'em if you dare.

[will]

That's something I've been searching for...specs for the stock motor/ESC.

I don't wanna postjack, but... Hey Miami guys, ever had a stock ESC die due to heat? I've been thinking about coming up with some kind of heat sink for it. It's hot up here, but not like Miami.

[flydiver]

It's not so much the ESC (probably) as the BEC.
The BEC needs to drop the voltage to 5V for the servos and RX. A linear BEC uses resistors > makes heat. The higher the voltage > the more heat it makes. If it's already hot out it has less ability to dissipate the heat. I think Dillzio put a heat sink on a stock ESC. Some things are just hardly worth the effort though.

You can try calling HZ but don't expect an answer. I did, twice. Nice folks, either cannot or will not divulge that info. I KNOW that they KNOW it, because they are very careful to set their systems up properly for RTF. SOMEONE DOES know it. They just aren't telling. They almost NEVER admit mistakes and are AMAZINGLY generous in freely fixing the stupid a$$ mistakes of newbies, but they don't divulge electronic specs for RTF.

[Silverback]

Mar 25, 2011 20:25:56 GMT 1 flydiver said:

I just re-read your question.
I answered it.
There are links to actual tests with different props and different voltages.
You want more data, get a wattmeter, test stand, tachometer, infrared thermometer, a bunch of props and have at it.

But let me repeat - HZ provides NO DATA AT ALL ON THESE PRODUCTS. It "appears" it is a 13A motor and maybe a 15A max ESC (maybe....on a good day, with cool temps and good ventilation). Those are lines in the shifting sand of HZ non-disclosure. Cross 'em if you dare.

where did anyone post anything about specific props???

and like I said in the original post:

Mar 9, 2011 22:42:35 GMT 1 Silverback said:

So I'm finding a lot of discussion for stock LP cub props, but a lot of that is also around how far can you push it and not burn out the stock electronics....

So again, I'm wondering
- stock motor
- aftermarket electronics (don't care to discuss what this really is)

Prop recommendations that will result in maximum thrust and relatively low pitch speed without burning up the motor. Looking at what numbers out there the stock setup appears to be setup for a pitch speed in the mid to high 5xmph range, for a plane that should have a stall speed in the low to mid teens, so if you can get good thrust at a pitch speed in the 35-40mph range yous should actually get a much more efficient combination and closer to "bush plane" type performance.

ALL the similar discussion that I've been able to find on this board discussed this within the context of what will not burn out the stock electronics, not the stock motor.

also,

Mar 13, 2011 2:13:14 GMT 1 flydiver said:

You can under prop. Often you gain some efficiency at the expense of some performance. This is not always a bad trade-off.

HUH?

Efficiency is generally defined as getting the maximum amount of work done with the same power input, or the same amount done with the least possible power output.

Underpropping seems to imply a smaller prop/pitch combination than what produces the most thrust for a given power input... that would by definition imply less efficiency then a better matched prop throttled back some to achieve the same thrust.

[flydiver]

See the link in my second post. Admittedly they are static power output curves. The challenges of getting efficiency data in a flying plane are not insignificant and I guarantee you will not find it in a 'newbie SC" thread. No one cares about the efficiency of a 480 brushed motor-likely not better than 65% anyway.

Start studying some power curves:
www.flybrushless.com/
This one for example:
homepages.paradise.net.nz/bhabbott/2205-15T.html
Notice how far 'back' on the prop curve the most efficient prop is (5x3). Most folks will actually prop it at 6x4 or 7x3.5, if not 8x4 in an attempt to get everything out of it they can.
or

you may like playing with one of these programs:
brantuas.com/ezcalc/dma1.asp
www.motocalc.com/

Underproping as I define it is trying to find prop size for the motor where you get the most flying time out of a particular power setup (ignoring thermals and coasting). It's like finding the speed for best mpg in your car, likely about 45mph. NO ONE drives 45mph on the freeway, so very few folks actually go for maximum efficiency. This crowd goes for maximum power.

Remember, electric motors are not gas motors. Maximum torque is near stall. Maximum efficiency is near unloaded top RPM. In real world flying we tend to prop them about 75% of unloaded RPM-that's the optimum user experience, kind of like driving 60 on the freeway. Slower is a drag but more efficient. Faster gets you there quicker but mpg goes rapidly down hill.

If you really just want EFFICIENCY I suggest you prop it with a prop that will just barely fly it at full throttle with the battery 3/4 spent. The slower you go through the air the less turbulence, less friction, less drag. You will also be working the motor less hard. It might be spinning fast but it won't be working hard. Electric motors don't care a whit about that. You won't have to worry about burning out the motor, or electrics, at all.

You will learn but you may not get what you are after. I helped a buddy find the best power:thrust for a particular setup out of a handful of suitably sized props he brought over. One was a clear winner. It was a GWS thin electric. At the field he didn't like it. He had to 'wind it up' too much to suit him. He put on a big slow fly and was happy probably at the expense of a 10-20% loss of efficiency. Who cares, this is for fun.

[Dillzio]

Silver, for the sort of characteristics you want, you want a very low pitch prop. Every prop has a maximum speed, or "pitch speed". The higher the pitch, the faster it tries to make the plane go. The closer you get to the pitch speed, the less work the prop has to do, so the less power you'll use (once you get near your pitch speed, the prop is basically windmilling).

The most efficient prop you can use will be one with the lowest pitch that can do the job. I'd recommend a 9x5, but if you need more power than that, then increase diameter but still keep the pitch as low as possible.

OH, BTW, the stock SC prop is 9x6, not 9x8, but it's a slow-fly style prop so it generally puts out more thrust for less power than a more robustly built prop. Generally speaking, you can't put a slow-fly prop on a plane like the super cub, not unless you don't mind the prop self-destructing at max throttle due to exceeding it's maximum RPM. The stock one that comes with the cub must be a particularly high quality slow-fly prop to be able to handle a 3s lipo.

You don't want to use a 3-blade prop, they are less efficient than 2-blade props. The only reason you'd ever use a 3-blade is if a 2-blade would be too big (such as on the corsair).

[Silverback]

Aerodynamically, a 3 bladed prop should be somewhere in the range of 3% less efficient than a 2 bladed... I'm not sure why people are so against that, since it seems that maximum thrust should actually happen with a larger OD prop and lower pitch, and a smallish plane like the SC just doesn't have the room to spin say a 12 (and maybe an 11") prop. If you could get the thrust of 97% of a 11" prop from a 10" 3 blade, I'm not sure why not to do it. In this range you're typically talking about 15-30oz thrust, which means the 3 blade would have 14.55-29.1oz. I wouldn't be surprised if you see a bigger difference between 2 of the same size prop in some cases.

[Silverback]

Mar 26, 2011 4:45:32 GMT 1 flydiver said:

Start studying some power curves:
www.flybrushless.com/
This one for example:
homepages.paradise.net.nz/bhabbott/2205-15T.html
Notice how far 'back' on the prop curve the most efficient prop is (5x3). Most folks will actually prop it at 6x4 or 7x3.5, if not 8x4 in an attempt to get everything out of it they can.
or

you may like playing with one of these programs:
brantuas.com/ezcalc/dma1.asp
www.motocalc.com/

Underproping as I define it is trying to find prop size for the motor where you get the most flying time out of a particular power setup (ignoring thermals and coasting). It's like finding the speed for best mpg in your car, likely about 45mph. NO ONE drives 45mph on the freeway, so very few folks actually go for maximum efficiency. This crowd goes for maximum power.

Remember, electric motors are not gas motors. Maximum torque is near stall. Maximum efficiency is near unloaded top RPM. In real world flying we tend to prop them about 75% of unloaded RPM-that's the optimum user experience, kind of like driving 60 on the freeway. Slower is a drag but more efficient. Faster gets you there quicker but mpg goes rapidly down hill.

If you really just want EFFICIENCY I suggest you prop it with a prop that will just barely fly it at full throttle with the battery 3/4 spent. The slower you go through the air the less turbulence, less friction, less drag. You will also be working the motor less hard. It might be spinning fast but it won't be working hard. Electric motors don't care a whit about that. You won't have to worry about burning out the motor, or electrics, at all.

You will learn but you may not get what you are after. I helped a buddy find the best power:thrust for a particular setup out of a handful of suitably sized props he brought over. One was a clear winner. It was a GWS thin electric. At the field he didn't like it. He had to 'wind it up' too much to suit him. He put on a big slow fly and was happy probably at the expense of a 10-20% loss of efficiency. Who cares, this is for fun.

that would probably come closest to answering my question, what big, slow fly or similar pitch (probably in the 4-6 range) prop would work best without frying the motor?

Those links point out a problem with what you've written... taking that first example the best thrust/watt numbers are for the 7035 prop, but since thrust is a force without a velocity there is no efficiency, and the calculated efficincy numbers on the graph are useless for this discussion. They are calculated using torque and rpm to compute power output of the motor and comparing it to the power input, not sure why they would even bother besides that is a number they can give you. It doesn't account for how efficiently the motor/prop combination converts the power input to the power output (available to move the plane). Where the motor is most efficient is not where the motor+prop combination is or what motor+Prop combination is.

[Dillzio]

3% huh? I had no idea it was so low, I just read somewhere that they're less efficient. You're right, 3% is nothing, you would be likely to see more difference in two different props of the same diameter and pitch. I consider my margin of error for testing in my relatively crude setup to be about 5%, so 3% i wouldn't even notice. What size 3-blade are you thinking of going with?

[Silverback]

Dillzio, from my first post starting this thread:

Mar 9, 2011 22:42:35 GMT 1 Silverback said:

Secondly, I don't really care much about top speed, I'm adding flaps, flaperons, and may play with slats/vortex generators/more wing area. It's got big tires on it and want bush plane type performance.

Any recommendations on prop (brand/style/size)? I'm almost tempted to try something in the 11x4.7 or 5.5 range (Not really sure that I have the ground clearance to not break one), or maybe even a 3 blade, 10x5 or something

but I still don't know if practically an 11" prop will clear or if either it or a 10" will cook the motor...

[flydiver]

With 3" wheels and a smooth surface you probably could get an 11" going.
No problem at all with a 10" since the old stock NiMh prop is 10" (10x8) on stock wheels

I steered you wrong with the 6x4 idea. The concept I was trying to get across was to let the motor "run" (wind up, little load) with as low airspeed as possible.
Dill pointed the right direction > a large prop with low pitch. Large slow moving props are more efficient than small props moving fast. Try a 10x3.8 APC slow fly. (Don't bother with the GWS 10x4.7SF, it might blow up-very flimsy).

There are larger low pitched ones available also:
www.bphobbies.com/view.asp?id=V766841

But you do have the issue Dill points out > [Maximum RPM is 65,000 / Prop Diameter in inches - for APC SF]
I have no idea if you are approaching this with 11 and 12 inch SF props on the Cub. I don't have a stock setup to test anymore and most folks that do won't have the test tools.

As pitch goes down, load goes down. You certainly won't be over taxing the motor on a 10x3.8, probably not even on an 11x3.8, maybe not even a 12x3.8 but I've never seen any tests. You also might be pushing RPM limits.

[Dillzio]

As long as you run 2S props of 10" or bigger, that should keep your rpms low enough to use most slow-flyer props.

This is a different type of SF prop that should be fine on 2S.
www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5296
www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10394

This one comes in 11x3.8 if you want more power (and don't repeat that you've said you're not that worried about power, it's becoming tiresome)
www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6226

Testing if you're overtaxxing the motor is not difficult, run the prop for one minute then see if the motor's hot, then run the prop for 5 minutes and see if it's hot. The props are only about $1 each so you may as well buy a few different sizes to experiment with.

Fly's suggestion of the 10x3.8APC slow-fly is about as good a tip as you're likely to get mate.

[Silverback]

how fast can you spin a slow fly prop?

(I don't think that I've said I'm not worried about power, more power at a reasonable pitch speed is exactly what I'm after... edit- as long as the pitch speed is in a reasonable range, say under about 35mph or so the post power i can get without burning up the motor is what I'm after, of course, that may be the same or slightly less total power than a higher pitched prop might make since power is proportionate to thrust x speed)

[flydiver]

APC > [Maximum RPM is 65,000 / Prop Diameter in inches - for APC SF]

GWS > Does not publish data. Much more flexible. Got to be lower. You can hear them go bad as they start to flex when the RPM gets too high.

Hobby King > You got to be kidding!

The rest > no idea, start researching

Do you have a tach? Wattmeter, tach, and IR thermometer (or digital 'finger') are necessary tools for this kind of work.

[Silverback]

Playing with webocalc (seems to suggest that I want to keep the pitch around 5...) and I could rig something if I had to (o-scope and a photocell...) or i can borrow an optical...