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Old Jan 06, 2013, 08:40 PM
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Originally Posted by ashdec87 View Post
The windmilling prop does cause a huge amount of drag
...says you
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Old Jan 06, 2013, 08:52 PM
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Lol it does. Supposedly the same mount of drag as a solid disk the same size as the prop. Which is why full scale planes must feather a dead engine.
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Old Jan 06, 2013, 10:00 PM
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See, and to me that makes zero sense. A spinning prop doesn't magically increase in surface area to that of a disc. At any given time, the same amount of prop is confronting air. The only question is with how much resistance it hits the air. A spinning prop at least gives way.

Now, I know that full scale planes do feather dead engines, but from what I've read, there's a point at which the combination of mass/airspeed/surface area of prop create a tipping point, where it's better to windmill than to brake.

Not being a physicist, all I know is this: setting the brake on an ESC is one more step between me and flying, and after a day of trying with/without brake on multiple wings, I noticed absolutely no difference. That's why I say let 'er swing.
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Old Jan 06, 2013, 10:08 PM
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Well, i don't mean to feed the fire.. ive seen this discussion before.. but i always think of auto gyros.. maybe it's a whole different can of beans I say if you are that worried about aerodynamics to be concerned about spinning props or not, just get a folding prop and be done with it
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Old Jan 06, 2013, 10:11 PM
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Originally Posted by elCapitan View Post
Not being a physicist, all I know is this: setting the brake on an ESC is one more step between me and flying, and after a day of trying with/without brake on multiple wings, I noticed absolutely no difference. That's why I say let 'er swing.
Lol exactly. Short of being in a gliding competion, I don't think there's an advantage for the brake.
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Old Jan 07, 2013, 03:54 PM
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Originally Posted by elCapitan View Post
and after a day of trying with/without brake on multiple wings, I noticed absolutely no difference.
I've had the same experience. However, Google does reveal support for ashdec87's statements, no matter how non-intuitive. The studies I found involve twin engine planes when one engine quits. The pilot wants to continue flying on one engine, which means the dead engine's prop is going to want to turn almost the same speed as the engine that's running. To do that requires a LOT of power, hence a lot of drag.

We're not doing that with our planes. Usually the only time we're power off is landing, when more drag slows the plane down, usually what we want. I suspect at the lower speeds, the difference becomes negligible.
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Old Jan 07, 2013, 07:22 PM
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That's true, we're flying at 30mph tops, those planes are going 150+
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Old Jan 07, 2013, 08:22 PM
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And they can probably feather the blades as well, we can not
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Old Jan 07, 2013, 11:19 PM
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Originally Posted by michaelingp View Post
The studies I found involve twin engine planes when one engine quits. The pilot wants to continue flying on one engine, which means the dead engine's prop is going to want to turn almost the same speed as the engine that's running. To do that requires a LOT of power, hence a lot of drag.
Right, but you're talking about a completely different motor, not a brushless. Even if you scaled down in size, the force required to spin a prop on one of those engines, due to friction, is a lot more than one of ours needs. That's the only reason it requires a lot of power in that scenario.

So not only does it make less difference at low speeds, but also at low internal friction in the motor.
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Old Jan 08, 2013, 01:43 PM
Lee
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Originally Posted by ashdec87 View Post
That's true, we're flying at 30mph tops, those planes are going 150+
Actually we clock the Reaper at an actual speed of 80+ mph with the 3530-1700 kv and some flyers going 4S are over 100 mph and I have heard of 6S over 120 mph. It's all a power to drag/weight ratio. Just make sure you use big servos and reinforce your linkages if you go this fast.
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Old Jan 08, 2013, 05:29 PM
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Actually we clock the Reaper at an actual speed of 80+ mph with the 3530-1700 kv and some flyers going 4S are over 100 mph and I have heard of 6S over 120 mph. It's all a power to drag/weight ratio. Just make sure you use big servos and reinforce your linkages if you go this fast.
i think mines pushing around 65 at top speed easy, it cruses around 35-40 maby. im still dialing it in, i flew it this morning the adjustments i made, made it fly alot better.
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Old Jan 08, 2013, 07:20 PM
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Ok, need some collective input here, I have the 3536-1800kv motor. I went ahead and got a 80a esc since they claim the motor pulls max 60 whatever amps. I do have intentions on flying at a higher cruise speed and I am wondering if I can partially embed the esc into the wing and leave the top heat sink portion exposed? I just want to bury the bottom and the sides. Last time I flew the motor was warm but the esc was not. What do you guys think?

Eric
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Old Jan 08, 2013, 07:24 PM
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That's exactly how my DRXL is set up, with the same motor and same size esc. No problems yet.
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Old Jan 08, 2013, 07:26 PM
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Originally Posted by E1Allen View Post
Ok, need some collective input here, I have the 3536-1800kv motor. I went ahead and got a 80a esc since they claim the motor pulls max 60 whatever amps. I do have intentions on flying at a higher cruise speed and I am wondering if I can partially embed the esc into the wing and leave the top heat sink portion exposed? I just want to bury the bottom and the sides. Last time I flew the motor was warm but the esc was not. What do you guys think?

Eric
"Not", or "Hot"? i wouldn't see any reason to mount that way if the ESC wasn't even warm..
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Old Jan 08, 2013, 07:45 PM
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That's how I mount all my esc's, either glued in that way, or with lam over the top. Only trouble I've had with an esc was the one I dunked in a lake
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