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Old 01-11-2008, 12:53 PM   #1
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Default 9Y Brushless on Slow Stick - What Prop?

Hi:

I got one of those 9y motors from BP. I just put it on a Slow Stick. I have a three cell Lipo battery with 1300 MaH. The plane is built stock.

The speed control is an 18 AMP BP yellow one.

I got some 10/4.7 props but am looking on line and thinking that I have to use a different prop?

What prop should I use with this setup?

Thanks.

Michael
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Old 01-11-2008, 01:09 PM   #2
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You are good. That will give you about 22 oz thrust using about 10 amps and a pitch speed of around 28 mph. You could also use a larger prop and gain a little on everything, but not much. On that same motor, I've used a GWS 1060 and an 1170. The 1170 will try to fly it a lot faster if that is what you want.
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Old 01-11-2008, 01:19 PM   #3
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Boy, thanks for that detailed answer.

How the heck do you figure this stuff out? Is there a formula? Sure would be nice to know how to figure all this out in advance.

Thanks again.

Michael
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Old 01-11-2008, 02:13 PM   #4
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The information is available from many sources and can be very confusing.

Try www.headsuprc.com Jeff has a lot of information available that will help you. Click on your motor and scroll down.

There are a lot of others, but headsuprc gives the information in a very clear manner.

I'm not associated with him in any manner except that I've been a customer.
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Old 01-12-2008, 05:13 AM   #5
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Along these same lines...

I just finished my Slow Stick. I put on the same 2410-09Y motor I bought from Jeff. His recommendation was to use an 1147 prop, but I mistakenly bought 1047 instead.

I know the 1047's will do, but could someone tell me what the difference in performance, current, wattage, and flight duration would be between the two props.

I don't need actual figures, just something like:
You'll get more speed with xx47 over the yy47.
The xx47 will draw more current than the yy47.
etc.

I hope you understand what I'm asking for.
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Old 01-14-2008, 06:14 AM   #6
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DO NOT go by recommendations... you must measure things. Due to small variations in the motor and differences in altitude, you could easily fry your motor using a setup that works fine for someone else, or you could end up with a setup that isn't powerful enough to fly your plane. I was bitten twice by this before I got a power meter and learned to figure it out myself.

Basically, since you have already picked the motor and battery, you get a selection of different props and hook them up and measure the amp draw with your meter until you find the prop that gives you closest to the limit of the motor.

Here's how it works...
Higher pitch with increase the speed.
Higher diameter will increase the thrust.

Both of these thing will increase the amp draw against the motor.

So, if you start with a 10x4.7...
A 10x6 will give you more speed and more amps.
A 11x4.7 will give you more thrust and more amps.

There are also different types of props, Slow Flyer, Thin Electric, etc... and they are all different... so, an APC Slow Flyer 10x6 might give you 100 watts with a given setup, but the Thin Electric might only give you 75 watts... while the Master Airscrew would give you 90 watts...

Also, a given setup might pull 100 watts here in Denver, but 150 watts in Phoenix... if I move to a different town, I'll have to measure everything again and change all my props.

These are not actual numbers, just estimates... are you seeing why you need to measure it yourself?

Get your Strykers and come on y'all... let's have a furball!
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Old 01-14-2008, 03:27 PM   #7
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Well.....yes, you are correct, but some simple begginer setups, with simple motors don't really require a large expenditure of finances to enjoy. If you are trying to wring every ounce of performance from your plane, or are trying to fly on the edge of the power envelope, yep, you will need more equipment. And I agree that folks that stay in the hobby should buy the equipment eventually, but a lot of folks just want to fly and aren't sure if they will stay with the hobby.

I don't see him burning up his slow stick motor with any of these props, and I also can't see purchasing a watt meter for a slow stick.

The suggestion to measure is a good one though. Maybe ask around the field and see if someone has a power meter that will measure your set up for you.
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Old 01-14-2008, 03:42 PM   #8
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My idea when making that post was to try to grasp the general concept of the differences in prop pitch and length.

I think I gave too much information in specifying a particular plane, but let me see if I understand what you've said so far...

(Forget about a plane. Lets just assume a motor will move through the air when it turns the prop.)

You stated:
"Here's how it works...
Higher pitch with increase the speed.
Higher diameter will increase the thrust."

So, (Bold are my words trying to understand the statement.
  • Higher pitch with increase the speed because the prop will cut deeper into the air in front of it.
  • Higher diameter will increase the thrust because the prop will grab more air around it.
  • And in each case the motor will draw more amps because it has to work harder.
I actually may start a new topic dedicated specifically to this subject.
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Old 01-14-2008, 03:47 PM   #9
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Originally Posted by cliffh View Post
Well.....yes, you are correct, but some simple begginer setups, with simple motors don't really require a large expenditure of finances to enjoy. If you are trying to wring every ounce of performance from your plane, or are trying to fly on the edge of the power envelope, yep, you will need more equipment. And I agree that folks that stay in the hobby should buy the equipment eventually, but a lot of folks just want to fly and aren't sure if they will stay with the hobby.

I don't see him burning up his slow stick motor with any of these props, and I also can't see purchasing a watt meter for a slow stick.

The suggestion to measure is a good one though. Maybe ask around the field and see if someone has a power meter that will measure your set up for you.
Excellent summary, Cliff.

I do hope to eventually get the various pieces of test equipment, but being retired and on a limited income things like that (and a new radio) have to be purchased gradually.

I do fly with some friends who should have a watt meter. I'll ask them to bring one next time we get together.
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Old 01-14-2008, 03:49 PM   #10
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You are correct, and also, like Jasmine said, the only way to know how MANY amps the increase was, is to MEASURE.

She also correctly mentioned that the same diameter/pitch prop of different style will produce different thrust/amp draw. THAT is where the real confusion starts for me
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Old 01-14-2008, 04:37 PM   #11
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Originally Posted by cliffh View Post
...

She also correctly mentioned that the same diameter/pitch prop of different style will produce different thrust/amp draw. THAT is where the real confusion starts for me
Didn't think of that when I mentioned starting a new topic on this subject.

I wonder if I start a topic on props that there will be so many variables a general rule of thumb can not be agreed upon?
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Old 01-14-2008, 07:06 PM   #12
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Originally Posted by Sir Raleigh View Post
Didn't think of that when I mentioned starting a new topic on this subject.

I wonder if I start a topic on props that there will be so many variables a general rule of thumb can not be agreed upon?
There is a sticky - something about "Choosing a power system" - and we have all written tons of information in there about this stuff. The reason I give such a stern warning is because I burned up two motors using the exact setup that was recommended by the maker.

I got a 400XT motor, and was told that I could run it with a 10x3.8 Slow Flyer and 3-cells of Lipo, so that's how I set it up. And this guy is in Colorado, so he's at the same altitude. Anyway, I was out flying and as soon as I went to full throttle for a loop or something, I noticed a strange sound, so I pulled back on the throttle a bit and did a low pass... very weird sound... so I landed. Upon inspection I realized that the motor wires had melted all the way out to the bullet connectors, and the bearing got so hot that it popped out.

So I sent the motor back and I called the guy and I confirmed that I was running the proper setup, and he said yeah it should be fine, I'll replace the motor for you, it must be defective. So when I got the new motor I put the same prop on there and tried it again... same result. As soon as I went to full throttle, the motor melted.

Our altitude is the same, and our batteries are the same, even same ESC and same plane. His motor is fine and mine were both fried instantly. So there must be some kind of small variation in the motor. This is why I say you have to measure it. I would have gladly paid the $50 for a power meter if I had known at the time that it would help. It would have been worth it even though I didn't pay for the replacement motor... I was stuck with the second one, and I was grounded for two weeks.

The photos are what happens if you use the wrong prop. That magnet wire is supposed to be clear and shiny (like in the last picture where I'm re-winding it)... not black and burned. If I had not landed right away, it could have damaged my ESC and battery, and that gets expensive.


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Get your Strykers and come on y'all... let's have a furball!
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Old 01-14-2008, 08:14 PM   #13
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Goofey: It's kind of understood that it's bad form to keep starting threads on the same topic in different locations. I thought we had finished this.
If you are that concerned buy a watt meter and test the set up. Cost will be $55.00 and up. There are endless threads on the best, just keep in mind we are discussing a set up that cost a bit less that $32.00 I have spent much more than that on one Carbon Fiber prop!
Go fly the thing!!!!!!!!
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Old 01-14-2008, 08:41 PM   #14
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Well Flashburn, I certainly can't argue with a man who's got it all.

Michael
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Old 01-14-2008, 08:57 PM   #15
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You can always try the 'finger test' - run the motor up to full throttle for about 5 seconds, then stop it and feel it... if it's hot, then you're going to burn it up. If it's not, then run it up again for 10 seconds and check it again... then try it for 30 seconds and check it again. If you can run it at full throttle for 60 seconds without it getting hot, then it's fine. There is no way to tell if it's giving enough power that way, but it will burn your fingers if it's getting too much. A power meter will tell you if it's getting enough power to fly, otherwise you'll just have to put it in the air and see if it has enough.

Get your Strykers and come on y'all... let's have a furball!
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Old 01-14-2008, 08:59 PM   #16
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I started to write a little about props and motors and efficiency and so on, but it's all physics and stuff and you might find it boring, so I put it on my blog.

This is the long explanation of how propellers and motors use energy and what is really happening when you try different diameters and pitches.
http://jazzyflight.blogspot.com/2008...ropellers.html

Get your Strykers and come on y'all... let's have a furball!
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Old 01-14-2008, 09:24 PM   #17
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[quote=jasmine2501;338250]
(snip) His motor is fine and mine were both fried instantly. So there must be some kind of small variation in the motor. This is why I say you have to measure it. [quote]
(snip)

I read your blog and you have some very good information there.

I own a watt meter by the way use it quite a bit.

In your case though, I'm not that sure it would have done any good. It really appears that you got two bad motors, probably out of the same batch. If his motor (with identical setup and altitude) worked just fine, and your motor(s) fried that quickly, something else was going on. I'm thinking that your watt meter would likely have just told you that everything was in spec. as your motor turned to smoke.

The meters won't help with that type of problem. An example would be that you expect the motor to draw 12 amps....and it draws around 12 amps....you would think everything is okay.....until you see the smoke.

When rewinding the motor, did you find any clue as to why the motor burned up?
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Old 01-14-2008, 10:01 PM   #18
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Originally Posted by cliffh View Post

When rewinding the motor, did you find any clue as to why the motor burned up?
Other than it being really thin 3-play wire, no... no clue. With a 10x3.8 on a similar motor I was getting 13 amps, so I think it was just too much prop. I run a 9x4.5 Thin Electric on that setup now, and that comes in at 9 amps, so it's been nice and reliable.

Get your Strykers and come on y'all... let's have a furball!
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Old 01-15-2008, 09:51 PM   #19
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Jasmine's right, a meter is probably the most important tool to have if you are going to stay in electric. A good meter will save you a ton of money down the road.

Case in point here, I would have told you a 12 x 6 as that's what I run on mine. Others mentioned different sizes, the only way to know is to meter each set up at wide open throttle. WOT will give you the most accurate idea of what's going on, using any other throttle positon will tend to be off as the meter averages it readings and will give you a lower reading then actuallity.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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