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Old Jan 25, 2012, 11:23 AM
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Hi (again) all,

Been busy with a Turnigy 9X flashed to ER9X - wow, it's impressive (Thanks wheelspinner)

I have a Polaris question about the CG.

I'm in the middle of a 133% or so Polaris (wingspan 39" as it's all I could get the printer to print after ages). I know it should balance around the step but I've tried right side up and upside down. In both cases, when I think it's balanced, I can tip it either fully forwards, or fully backwards. Does that mean the CG is right.

Another thing happened was I put the 2212-6 motor on a wattmeter and pull scales. Here's what I got:

6 x 4 130 watts 100g = .77g per w
7 x 4 297 watts 600g = 2.02 g per w
7 x 4.5E 310 watts 610g = 1.96 g per w
7 x 5 260 watts 650g = 2.5 g per w
7 x 5 230 watts (lwr v?) 22 amps 620g = 2.69g per w

I wouldn't have thought that this was possible from a motor that size? How are you all using a 6x4 prop when the output is so small?
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Old Jan 25, 2012, 11:45 AM
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Quote:
Originally Posted by Luke2000 View Post
Hi (again) all,

Been busy with a Turnigy 9X flashed to ER9X - wow, it's impressive (Thanks wheelspinner)

I have a Polaris question about the CG.

I'm in the middle of a 133% or so Polaris (wingspan 39" as it's all I could get the printer to print after ages). I know it should balance around the step but I've tried right side up and upside down. In both cases, when I think it's balanced, I can tip it either fully forwards, or fully backwards. Does that mean the CG is right.

Another thing happened was I put the 2212-6 motor on a wattmeter and pull scales. Here's what I got:

6 x 4 130 watts 100g = .77g per w
7 x 4 297 watts 600g = 2.02 g per w
7 x 4.5E 310 watts 610g = 1.96 g per w
7 x 5 260 watts 650g = 2.5 g per w
7 x 5 230 watts (lwr v?) 22 amps 620g = 2.69g per w

I wouldn't have thought that this was possible from a motor that size? How are you all using a 6x4 prop when the output is so small?
The watts per Gram is't so..
I beleive you'll find a 34Oz. Plane will fly really well with the recomenden motor and ESC..
Headsup rc .com has a 2200 kva motor and tested it with the proper prop and acheived ???? OZS. OF THRUST,,,,, much higher then your cart explains??
Look once as it has been how I figure to build a lot of of planes..
There are some loss with thrust due to prop size,,apc or plastice slow fly,, and weight< and .,,,
The amp draw will go up..
Just saying??
Later ,
Lenny
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Last edited by lennyboy; Jan 25, 2012 at 12:07 PM.
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Old Jan 25, 2012, 11:50 AM
60 years of RC flying
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Canada, ON, Ottawa
Joined Feb 2006
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Quote:
Originally Posted by Luke2000 View Post
I'm in the middle of a 133% or so Polaris (wingspan 39" as it's all I could get the printer to print after ages). I know it should balance around the step but I've tried right side up and upside down. In both cases, when I think it's balanced, I can tip it either fully forwards, or fully backwards. Does that mean the CG is right.

Another thing happened was I put the 2212-6 motor on a wattmeter and pull scales. Here's what I got:

6 x 4 130 watts 100g = .77g per w
7 x 4 297 watts 600g = 2.02 g per w
7 x 4.5E 310 watts 610g = 1.96 g per w
7 x 5 260 watts 650g = 2.5 g per w
7 x 5 230 watts (lwr v?) 22 amps 620g = 2.69g per w

I wouldn't have thought that this was possible from a motor that size? How are you all using a 6x4 prop when the output is so small?
It should balance AT the step or 1/4" ahead.

You can't determine CG by sitting the model on its bottom. I simply mark the step location on both sides of the fuselage above the wing and pick it up with finger and thumb. Find the location where it balances level (ignore any instructions that say it should balance slightly nose down -- to find the fore-and aft CG it must balance level). This will give you a good fix on the CG.

If you want more precise measurements (not needed) you can make a stand with two rounded dowels sticking up on which to balance the model. Balance will be the same upside down or right side up, but obviously it won't sit there stably upright as the CG is above the pivot point.

On the thrust measurement, there's something wrong with the numbers for the 6x4. An APC 6x4 should turn 18,500 to 19,000 RPM and pull 22-23A static and 20-21A in the air. This corresponds to around 220-230 watts. The thrust is about 28-35oz. Hence the excellent performance, including accelerating vertical climbs in the 100% Polaris. With the XL, you can expect more modest performance but still get a quick takeoff and 45 degree climb (as long as the model is a reasonable weight -- mine is 32oz with that motor and 2200 30C battery).

Not sure why your data for the 6x4 is way off. Is that a proper APC thin electric prop? You can't use slow flier props on these motors.
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Old Jan 25, 2012, 12:00 PM
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Originally Posted by wijwoj View Post
Hey leo.geo,

I got my bits from giant cod here in the uk. They are very quick and good value. They have a motor which is pretty damn close to the one recommended by all here:

Motor - http://www.giantcod.co.uk/221206-220...-p-402397.html
Prop - http://www.giantcod.co.uk/6x4e-sport...-p-403325.html
Battery (30C could go for cheaper 20C if you want) - http://www.giantcod.co.uk/gens-2200-...-p-406466.html
ESC - http://www.giantcod.co.uk/hobbywing-...ller-p-42.html

Cheers,

Wij.
That motor looks like a good equivalent to the standard Suppo 2212-6. The ESC has a good reputation I've heard. For a standard size Polaris, I use a 20C 2200 battery as the 30C is getting pretty heavy. So it's not only cheaper but more suitable. Prop should be fine.
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Old Jan 25, 2012, 12:13 PM
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United Kingdom, England, London
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Originally Posted by Daedalus66 View Post
That motor looks like a good equivalent to the standard Suppo 2212-6. The ESC has a good reputation I've heard. For a standard size Polaris, I use a 20C 2200 battery as the 30C is getting pretty heavy. So it's not only cheaper but more suitable. Prop should be fine.
Ah right, thanks for the info Daedalus. I actually also have a 20C on mine, but saw that prices had gone down on all the bats so thought I would suggest a meatier one. Didn't realise that more C equals more weight, but that does make sense.

Leo.geo, here's a 20C one from giant cod:
http://www.giantcod.co.uk/gens-2200-...-p-407317.html

Cheers,

Wij.
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Old Jan 25, 2012, 12:27 PM
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luke....either your battery was dead or something like that OR maybe prop was on backwords?? d66 numbers have been repeated over and over within 5% or so on most of the posted standard setups. on a 3s 25c and up healthy battery. or maybe didnt have full throttle? not sure. since other prop numbers look in the ball park....im gonna go with backwords prop. ...
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Old Jan 25, 2012, 01:12 PM
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It wasn't the battery as this was the first prop I tried. I'm gonna do that test again and see. Maybe the backward prop syndrome all right.

I have a CG setup with the dowels and all, but what I'm finding is that it won't actually stay balanced at all! If I move the battery to the point where it appears balanced, it will tip either slowly nose down and then keep going down, or tip slowly backwards and then keep going backwards. I guess it's balanced at that stage but I have around 10 airplanes, and never came across one yet that won't stay at the balance point.

Thanks all

Luke
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Old Jan 25, 2012, 02:05 PM
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Originally Posted by Luke2000 View Post
It wasn't the battery as this was the first prop I tried. I'm gonna do that test again and see. Maybe the backward prop syndrome all right.

I have a CG setup with the dowels and all, but what I'm finding is that it won't actually stay balanced at all! If I move the battery to the point where it appears balanced, it will tip either slowly nose down and then keep going down, or tip slowly backwards and then keep going backwards. I guess it's balanced at that stage but I have around 10 airplanes, and never came across one yet that won't stay at the balance point.

Thanks all

Luke
try balancing inverted
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Old Jan 25, 2012, 02:17 PM
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Originally Posted by mt_flyer View Post
try balancing inverted
I tried that. It's a bit better upside down, but still just won't stay put. I'll see.

Regarding the prop, I tried again.

6 x 4 same as 1st time 155watts 15A 360g
6 x 4e 155w 14.5A 370g
7 x 4e (different prop to st test) 170watts 16A 510g
Don't think that any of them are genuine APC props though. I think that the sled the motor is mounted to jammed on the first 6 x 4 test.

At around 32oz. I think it's gotta be the 7 x 4 prop. Any suggestions?

Luke
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Old Jan 25, 2012, 02:32 PM
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Quote:
Originally Posted by Luke2000 View Post
It wasn't the battery as this was the first prop I tried. I'm gonna do that test again and see. Maybe the backward prop syndrome all right.

I have a CG setup with the dowels and all, but what I'm finding is that it won't actually stay balanced at all! If I move the battery to the point where it appears balanced, it will tip either slowly nose down and then keep going down, or tip slowly backwards and then keep going backwards. I guess it's balanced at that stage but I have around 10 airplanes, and never came across one yet that won't stay at the balance point.

Thanks all

Luke
Correct, if it's moving slowly back or forwards it's OK. More precise is not needed.

It means that your vertical CG (or better: center of mass) is between your wings. Which is good! Your other planes may be high wing models?
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Old Jan 25, 2012, 02:48 PM
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Polaris XL question

Is the Polaris XL pylon strong enough to support an 85 gram motor?
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Old Jan 25, 2012, 02:48 PM
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Canada, ON, Ottawa
Joined Feb 2006
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Quote:
Originally Posted by Luke2000 View Post
It wasn't the battery as this was the first prop I tried. I'm gonna do that test again and see. Maybe the backward prop syndrome all right.

I have a CG setup with the dowels and all, but what I'm finding is that it won't actually stay balanced at all! If I move the battery to the point where it appears balanced, it will tip either slowly nose down and then keep going down, or tip slowly backwards and then keep going backwards. I guess it's balanced at that stage but I have around 10 airplanes, and never came across one yet that won't stay at the balance point.

Thanks all

Luke
The backwards prop theory might explain things. What kind of prop was it?

Another possibility is that the ESC was not calibrated correctly for that run, so it wasn't reaching anywhere near full throttle.

Anyway, you don't need tests to determine whether it will fly. If things are set up right, the XL with 2212-6 at full throttle should have enough thrust to just about lift vertically out of your hands.

While batteries make a difference, there would have to be something seriously wrong with any 2200 (like a dead cell) to explain your numbers.

Re Balance

It doesn't need to stay balanced. What you describe simply shows that the vertical CG is above your balance point. Same thing always happens if you try to balance a low wing model right side up. But it doesn't matter (unless you let the model fall on the floor! )

All you are trying to do is find the longitudinal balance point. It's absolutely easy if you just pick up the Polaris by the fuselage with thumb and finger and find the point where it balances level. Takes about three seconds.

Having noted that the CG is too far forward, say, you move the battery back and try again. And so on till you have it right. Don't try moving the battery while balancing the model.

If you had no trouble balancing the others, they must be high wing models.
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Old Jan 25, 2012, 02:50 PM
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Originally Posted by bob93447 View Post
Is the Polaris XL pylon strong enough to support an 85 gram motor?
That's about the standard size. Mine currently has a 100g motor on it. No problem at all, though the battery needs to move ahead slightly for balance.
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Old Jan 25, 2012, 02:54 PM
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Originally Posted by Luke2000 View Post
I tried that. It's a bit better upside down, but still just won't stay put. I'll see.

Regarding the prop, I tried again.

6 x 4 same as 1st time 155watts 15A 360g
6 x 4e 155w 14.5A 370g
7 x 4e (different prop to st test) 170watts 16A 510g
Don't think that any of them are genuine APC props though. I think that the sled the motor is mounted to jammed on the first 6 x 4 test.

At around 32oz. I think it's gotta be the 7 x 4 prop. Any suggestions?

Luke
All those numbers are too low. With a 7x4, for example, you'd expect to see well over 20A.

So forget about measuring thrust and figure out why your motor is not drawing enough current. Take a good look at the ESC to make sure it's properly calibrated.

Exactly what props, motor and ESC are you using?
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Old Jan 25, 2012, 02:55 PM
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Originally Posted by mavlo77 View Post
Correct, if it's moving slowly back or forwards it's OK. More precise is not needed.

It means that your vertical CG (or better: center of mass) is between your wings. Which is good! Your other planes may be high wing models?
Great minds think alike. I didn't see this before I commented!
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