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Old Jun 19, 2012, 11:13 PM
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HoosierGuy's Avatar
United States, IN
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What Sized Prop for 2200KV Motor?

I've been enjoying electric gliders and planes so much that I bought a $12 brushless electric motor from Hong Kong off ebay. It had free shipping. I got it mostly to experiment with and play with. Anyway, I am thinking about putting it
in my Harbor Freight Wild Hawk. I have a new 40amp ESC and also a UBEC.

I'm wondering what kind of prop I should get for it. I don't have a watt meter yet.
Below are the details of my new motor. It does recommend a prop: 8040. But I'm not sure what that means. Also I would like to the opinion of others. This motor and prop would be used on my Harbor Freight glider with the motor/prop on top in back.

http://www.harborfreight.com/easy-to...ane-94774.html


Model No.: 2212-6
Rpm/V: 2200KV
Weight: 50g
Motor Dimensions: 27.7*26.3mm
Shaft Size: 3.17*37mm
Battery Opernating: 2-3 Lipo
Idle current: 1.8A
Load current: 18.5A
Power (Watt): 240
ESC(A): 30A
Ri(M Ω): 0.03
Prop/recom: 8040

Thanks
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Old Jun 19, 2012, 11:36 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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That's a common Suppo 2212/6 outrunner. They're sold in various places under various names, but they're really all the same and they're very popular for parkjets, wings, and planes such as the Wild Hawk, EasyStar, Bixler, and others with limited room for props.

The "8040" refers to a GWS HD 8040, which in "standard" nomenclature is an 8x4 prop. That would be a decent prop choice for the motor on TWO LIPO CELLS. For 3S operation, you'll want about a 6x3. The motor can take a prop with a bit more pitch, but on the WH that extra pitch would really just be wasting power and generating heat.
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Old Jun 19, 2012, 11:58 PM
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HoosierGuy's Avatar
United States, IN
Joined Jan 2012
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Since I want this prop to push my wild hawk, do I need a pusher prop? I'm not very up on props since I've not had to buy one yet. There is a difference between regular props and pusher props, right?
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Old Jun 20, 2012, 12:10 AM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
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Let's be extremely careful with this one...

Quote:
Since I want this prop to push my wild hawk, do I need a pusher prop?
No. You do not. Ignore anyone who says otherwise. They are wrong. Just wrong.

Quote:
There is a difference between regular props and pusher props, right?
Yes. A "pusher prop" is made so that its pitch is opposite that of a "regular prop". This is the ONLY difference, and it means that the prop will make thrust when spinning the opposite direction. It will make the same thrust and consume the same amount of power at a given RPM. An APC 6x3 and an APC 6x3P (for "pusher") are exactly identical with the sole exception that the "pusher" is a mirror image of the regular one.

The whole "pusher/tractor" designation is highly confusing and utterly useless with brushless motors. It's a carry-over from the days of glow engines that only ran one way, or ran better one way. "Normal-pitch" and "reverse-pitch" are more accurate and less confusing.

The prop doesn't know if it's "pushing" or "pulling". The only important bit is that it's mounted correctly, which is simple enough (but also really freakin complicated when dunderheads try to explain it).

Sorry for the rant. This particular topic has given me much grief when I try to explain it to others, and it doesn't help when forty other guys are spreading their incorrect information

I assure you that I'm right.
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Old Jun 20, 2012, 12:17 AM
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Yikes

I just realized how neurotic that last post sounds...

It's for a good cause.
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Old Jun 20, 2012, 12:24 AM
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Thanks for the info! So now I learned another thing about R.C. flying!
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Old Jun 20, 2012, 11:03 AM
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Australia, New South Wales, Sydney
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Totally agree with Mr. C4H10, but for the sake of completeness I wanted to add the counter-rotating scenario with a twin-engined aircraft. It is almost always better to have the two motors rotate in opposite directions, so that they cancel out each other's torque effects. Obviously, if one motor is turning clockwise and the other anti-clockwise, the two props cannot be identical. In that specific instance, one of the props should be a "pusher" so that it can do the exact same job - while rotating in the opposite direction.
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Old Jun 21, 2012, 10:39 AM
An Ordinary User
United States, VA, Fluvanna
Joined Jan 2011
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Also, I'd like to point out that HobbyKing sells them as CounterRotating props and GWS does too. In fact, I mistakenly bought some reversed props by mistake because I didn't understand the nomenclature.

GWS props
DD = Direct Drive
RD = Reduction Drive
RH = Right Hand Rotation

Also, some of the HK prop sizes have an "R" to indicate counter rotating such as 8x4.3R and 5x3R.

Even if you do like me and get the reversed props just mount them normally and reverse the motor. No problem.

I think the most common mistake people make is that they want to mount the prop facing themselves instead of facing forward in the direction of travel.

Normally, the side of the prop with the size/pitch information is facing forward. But I've got some props with no writing at all on them but there are dimples. I still don't know if dimples indicate the front of the prop or back...
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Old Jun 21, 2012, 02:14 PM
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Quote:
Normally, the side of the prop with the size/pitch information is facing forward. But I've got some props with no writing at all on them but there are dimples. I still don't know if dimples indicate the front of the prop or back...
The numbers-go-forward thing is ok in most cases (GWS, APC, MAS, GP, Graupner, Zinger, and many others) but there are a few odd props out there that have the numbers on the back or don't have them at all.

The one surefire way to know correct orientation is that the convex surface of the blade faces forward, that is, toward the direction of travel.
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Old Jun 21, 2012, 09:49 PM
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United States, IN
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Speaking of motors. What happens if you have a big crash. Then after repairs you put your motor in (lets say on the nose) and the motor/shaft looks a tad off center. The reason i ask is because I crashed my electric glider where the motor is on the nose. I had to fix the nose with fiberglass. The motor shaft is center when I examined it. But my fiberglass might be a little uneven on the firewall. When I put the motor on it's mostly straight but might be a little pointed to the left or right. But it is solid on the mount. How can a slightly crooked or more than slightly crooked mounted motor on the nose effect the glider?
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Old Jun 22, 2012, 04:47 AM
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HoosierGuy,

Generally all model aircraft motors are offset to the right and down a few degrees. The right offset is to counter the tendency of the aircraft to turn left due to the torque and prop wash over the vertical stabilizer. The down thrust is to overcome the tendency to climb under power.

So after your repair you should have a bit of right and a bit of down.

Glen
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Old Jun 22, 2012, 12:35 PM
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Quote:
Originally Posted by ggcrandall1 View Post
HoosierGuy,

Generally all model aircraft motors are offset to the right and down a few degrees. The right offset is to counter the tendency of the aircraft to turn left due to the torque and prop wash over the vertical stabilizer. The down thrust is to overcome the tendency to climb under power.

So after your repair you should have a bit of right and a bit of down.

Glen

Is that something you can fix through trimming/trim buttons?
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Old Jun 22, 2012, 12:57 PM
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Quote:
Is that something you can fix through trimming/trim buttons?
Nope. Trying that will just give you headaches because trimming the control surfaces will leave them in the same positions regardless of throttle setting.

The best way to set up your thrust angles is to use washers to shim the motor for a little down/right, then fly it and trim for level flight at cruise speed. When you cut the throttle and glide, the plane should keep going straight ahead and not pitch up or down severely. If it pitches down, you need a little more downthrust and a little less down trim.

The downthrust is usually quite a bit more important in my experience, but it does vary from plane to plane.
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Old Jun 22, 2012, 12:59 PM
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Quote:
Originally Posted by HoosierGuy View Post
Is that something you can fix through trimming/trim buttons?
Not really. If power was constant through out the flight you could do it with trim. However as you change power from take off to cruise and then to full throttle the required trim setting would change. The idea is to select the motor offset so that when the plane is in trim when gliding the change in power does not change the planes attitude. When properly trimmed and the motor offset is correct adding power will make the plane go faster but it will not pitch up.

Glen
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Old Jun 22, 2012, 03:08 PM
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United States, IN
Joined Jan 2012
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Quote:
Originally Posted by C₄H₁₀ View Post
The best way to set up your thrust angles is to use washers to shim the motor for a little down/right, then fly it and trim for level flight at cruise speed. When you cut the throttle and glide, the plane should keep going straight ahead and not pitch up or down severely. If it pitches down, you need a little more downthrust and a little less down trim.

What kind of washers? Aren't washers perfectly flat/smooth all around? Can you explain this a little more? Thanks.

Also, just got back from flying my glider, the one that I had to do the fiberglass job on. She flew pretty good although it was a little windy. Tomorrow is suppose to be nicer with less wind so I give it a good flying.
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