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Old Jan 26, 2012, 03:02 AM
Corflute Codger
flymess's Avatar
Australia, New South Wales, Fernmount
Joined Feb 2011
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Prop-wash causing inverted launch?

I built a corro delta with a shift in LE angle from 90* nose, to 60*wing area.
It flies nice once in the air but is hard to launch without it flipping upside down straight off.
Since then I added the small V-Tail to see if it breaks up and directs the propwash rearward.
My theory is that without the tail, the prop wash was pushing the very large, flat, plate-like surface clockwise from the rear, negating any torque roll.
Any thoughts people?Name: Photo on 2012-01-26 at 18.15 #2.jpg
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Last edited by flymess; Jan 26, 2012 at 04:00 AM.
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Old Jan 26, 2012, 11:55 AM
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I had an Aquastar did that. I just launched it at half throttle and it was ok.
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Old Jan 27, 2012, 05:23 AM
Corflute Codger
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Australia, New South Wales, Fernmount
Joined Feb 2011
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Quote:
Originally Posted by aspeed View Post
I had an Aquastar did that. I just launched it at half throttle and it was ok.
Thanks aspeed. the only time it did launch OK was at about 1/2 to 2/3 throttle so I must be getting carried away with the go stick on the last couple of tries.
Do you think the propwash theory washes?
I also dropped the prop size down from 6x4" to 5x5" to reduce the wash but have to wait for the rains to stop and the flood waters to recede before I can test it out
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Old Jan 27, 2012, 06:21 AM
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Sounds quite plausible to me. But I wonder if it is more torque reaction to the spinning prop when the plane is at low speed initially from the launch.
I usually launch at about 1/2 throttle or so and then power up as it gains a little airspeed. The control surfaces tend to not have much air moving over them at first. Albeit with a pusher, it is blowing air across part of the control surfaces. But the inner section doesn't have as much control as the outer sections have.
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Old Jan 27, 2012, 10:44 AM
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I'm with Earl, I think it would be more torque. Even with ROG takeoffs, sometimes you see planes want to roll like that initially until you counteract it and pick up some airspeed. Probably as a result of us typically over-powering our planes. There was an article in Model Aviation magazine a while back where the author was advocating putting some tip weight in the right wing to help prevent torquing on takeoff.
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Old Jan 27, 2012, 10:44 PM
Corflute Codger
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Australia, New South Wales, Fernmount
Joined Feb 2011
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I'm familiar with torque roll but this goes the opposite way. It's rolling the same way as the prop is rotating which leads me to the propwash theory. Floods have gone down so might be able to find out tomorrow if the changes I made will make a difference.
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Old Feb 02, 2012, 05:30 AM
Corflute Codger
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Australia, New South Wales, Fernmount
Joined Feb 2011
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Propwash

Well I managed to get some flights in despite the floods.
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Old Feb 02, 2012, 05:43 AM
Corflute Codger
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Australia, New South Wales, Fernmount
Joined Feb 2011
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propwash

Managed to have a few flys with the modifications. With the 5" prop and the V-tail there was no tendency to flip inverted even at WOT. Now to test which change made the most difference. (I know you shouldn't change more than one thing at a time but....)
So now I'll put the 6" prop back on and see if it flips at full throttle with a hand launch. Let you know
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Old Feb 02, 2012, 06:16 AM
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Awesome, glad you got it sorted out! Looking forward to the results.
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Old Feb 02, 2012, 07:01 AM
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I used to have a group leader that was training on carriers back when the Bearcats were the prop plane, so narrow gap here. But he said that if you had that in the chocks and nailed the throttle it'd pretty much roll over from the torque and had one instance when he was qualifying on a carrier that a pilot in front of him kept bolstering and got frustrated on his third attempt and slammed the throttle forward. Plane torque rolled up and over the conning tower. He figured it'd run into the side of the ship but the guy actually got off the throttle and back on gently in time to come into view in front of the carrier skimming the waves. He took it back to base. Told me the guy nailed the 3rd wire the first attempt the next day. My leader swapped over to helicopters.
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Old Feb 02, 2012, 11:29 AM
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I haven't done it myself yet. I keep meaning to give it a try, but I haven't yet. Anyway, I have seen some guys perform a discus throw with their wings and upon release the plane does a corkscrew like roll over, they simply continue the roll for 360 degrees and do a climb out like normal. It seems on the discus throw the planes have a natural tendency to roll like that. So it may be more common than one might think for the wings to have a roll tendency like what you are experiencing.
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Old Feb 03, 2012, 06:23 AM
Corflute Codger
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Australia, New South Wales, Fernmount
Joined Feb 2011
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Had another successful launch and fly with the 5" prop. Then wacked the 6" prop back on. Flew straight out of the hand even at WOT. No tendency to invert so I believe the little V-tail has done it's job. Tried it several times and not once did it flip over. I think I could have got it to launch without the V-tail with less throttle but being a heavy little thing (585gms = 20.63oz) it needs a lot of thrust to get going, so pretty hard to get it just right. But now very happy to have sorted it out and feeling a bit smug about it too. Nice to use the "noodle" and think things through to a happy conclusion. Thanks for everyone's input and suggestions. By the way, this is the plane I was wanting: capable of fast but also able to slow down. Woo-Hoo! For information, running Turnigy H2218-2500KV heli motor, HK 50A ESC & Turnigy 1800mAh 40C Bat
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