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« on: May 27, 2012, 12:38:52 PM »
karan3_k
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http://www.rcindia.org/self-designed-diy-and-college-projects/tricopter-setup-help!!!

This was the tri made by me, about 2 month back, in this vacc. i made few changes with the frame and found great change in the thrust.

previously i was using 3 blade 8*4 prop(http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5247) which i broke in a crash, so i used 2 blade 8*3.8 prop.(http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9842) which was lying in spare.
well when i actually did test flight the tri, which lifted at 60-70 throttle, now just jumps at 100% throttle,

i want to ask how much the "pitch" of prop affect the "thrust". i have done some search, that relation between rpm and pitch, so as if pitch increase by 1" rpm increase by 200.
well what is the conclusion?

what is the effect of pitch on "thrust"?

does no. of blade affect rpm or thrust?



and about the frame i attached strips of pvc sheets on landing support, which stop toppling and wobbling of tri while takeoff and landing.

i feet that this strip which lies below the motor is stopping the thrust provided by motors (attached pics will make me clear).

any1 having experience making frame of multi. please explain me.


plz explain abot prop and frame separately, i had experimented both distinctly.

2012-05-26 22.03.58.jpg
Understanding aerodynamics of prop and frame.
* 2012-05-26 22.03.58.jpg (65.87 KB, 800x600 - viewed 324 times.)
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« Reply #1 on: May 27, 2012, 02:27:00 PM »
hyd_quads
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AFAIK:
the diameter of the prop defines the thrust,
the pitch of the prop defines the climb-rate/upward lift-velocity

The pitch of the prop is something like this: If you have a 10X6 prop, the prop will 'travel' 6" forward per revolution
Notice a prop closely and you'll find that the pitch angle is greater near the centre and it is lower away from the center, because the tips of the props travel a 'better' circle than the inner part of the prop, there is a change in pitch angle so as to maintain a constant pitch throughout the prop.

I don't believe there is any effect of pitch on thrust, there's an effect only on the climb-rate.

The number of blades has little effect on the thrust. The thrust is greater on a 3-blade prop (than a 2-blade) 'provided it runs at the same rpm as the 2-blade prop'!, but we know, a 3-blade prop runs slower than a 2-blade on the same motor/engine. (of course, we need to consider the dia. and pitch of botht the props), so there is little difference.

I may be wrong somewhere, let seniors picth in.
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« Reply #2 on: May 27, 2012, 02:56:57 PM »
karan3_k
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thnx  hyd_quads that was very informative...  Salute

so if i want to pull more weight i need to increase no. of blades. or pitch & dia?

few more comments by senior plz
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« Reply #3 on: May 27, 2012, 04:03:14 PM »
hyd_quads
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I've heard 3-blade are more 'inefficient' than 2-blade props. I wonder how inefficiency is defined there. To pull more weight, i think you need to increase the dia. Smiley
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« Reply #4 on: May 27, 2012, 04:06:37 PM »
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so if i want to pull more weight i need to increase no. of blades. or pitch & dia?

I might be wrong but here is what i have read a lots of time in lots of forums (RCI & RC groups) motors with less KV (around 1000 - 700) along with higher pitch props give higher thrust.

So looking at the images i think this is the motor that you are using http://www.hobbyking.com/hobbyking/store/__5429__AX_2308N_1100kv_brushless_Micro_Motor.html

which is 1100 KV, so i guess 0905 props might be good producing good thrust, but it might get warm too. So that's my suggestion Thumbs Up Thumbs Up
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« Reply #5 on: May 27, 2012, 04:56:26 PM »
hyd_quads
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No satyagupta, I guess you got it wrong.

Quote
That's the point. The pitch differentiates the amount of forward movement the prop will create with one revolution. Hence lower pitch props are setup for thrust and higher pitch props are setup for speed.

the quote is from post #2 in http://www.rcgroups.com/forums/showthread.php?t=416945

Another guy says

Quote
large diameter & small pitch = more torque like a low gear in a car.
small diameter & large pitch = more speed like a high gear in a car.
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« Reply #6 on: May 27, 2012, 06:03:53 PM »
karan3_k
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I've heard 3-blade are more 'inefficient' than 2-blade props. I wonder how inefficiency is defined there. To pull more weight, i think you need to increase the dia. Smiley
well its not true for me,
0804- 3 blade worked great for me,

as i told 2blade 8*3.8 wasnt able to lift at 100% throttle, that former one did at 60-70% throttle...

from this i feel its not about dia, it can be pitch or no. of blade.
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« Reply #7 on: May 27, 2012, 06:10:53 PM »
karan3_k
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thnx for link it gives great info...

i think it answers me....
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« Reply #8 on: May 27, 2012, 06:37:55 PM »
hyd_quads
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well its not true for me,
0804- 3 blade worked great for me,

I said I didn't know how 'inefficiency' is defined there, but let me guess. I think he means to say that 3-blade props use up more battery to deliver the same thrust as a 2-blade prop. ineffiencey is about using up battery, not delivering thrust.. Just a guess. Not sure about it.
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« Reply #9 on: May 27, 2012, 07:08:40 PM »
Dharmik
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With same specs, 3 blade prop has more area than 2 blade prop due to one extra blade that's why it produces more thrust but balancing it is bit difficult.
Probably you can say
3 blade 8x4 prop = 2 blade 9x4
To increase thrust practically you have to try 9x5 or 10x4.5 prop. Type of prop also depends like APC, SF.
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« Reply #10 on: May 27, 2012, 07:13:40 PM »
hyd_quads
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@Dharmik: Yeah, the thrust increases becauses of the area, but the 3-blade prop will not spin with the same RPM as a similar spec 2-blade prop, so the net result may/may not be an increase in thrust. Not sure, though. :/
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« Reply #11 on: May 27, 2012, 07:25:45 PM »
Dharmik
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Yeah that's right, because we are adding extra load of one more blade(same specs of prop) and extra amp draw but other way we got much more area than two blade so we can ignore that small amount of load. We can compare it with gliders. They have long wingspan to get proper lift without engine.
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« Reply #12 on: May 27, 2012, 07:29:34 PM »
hyd_quads
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Okay.. thanks bro. Smiley
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« Reply #13 on: May 27, 2012, 09:26:45 PM »
karan3_k
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dharmik bhai i was expecting your reply.....

thanks @satyagupta and dharmik, i wil giv a try to 0905 prop....
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