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My planes seem to fly easier when power off ?
I've noticed this effect with several planes/motors now and can't see why - is it an illusion ?
With anything from IPS/1047 - geared 280/1180 - speed 400/folding 6x3 - When I switch the motor off at altitude the plane descends reasonably quickly and new trim is need -OK, that seems fairly normal. Coming in to land, when I switch the motor off , the plane seems to fly more easily - as if it was struggling before. At first I thought it was ground effect, but I have started turning off at higher levels, say 12 - 20ft and the effect is still there, most of the time. I run my motors in line, ie no downthrust. If my planes are struggling with power on it will be inefficient and I'd like to fix it. I think that adding downthrust will make the plane struggle more, but perhaps I'm wrong. All controls are trimmed to neutral and planes appear to be flying horizontal and look OK. Would any experts care to comment , please, thanks, Flyfan |
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What kind of planes?? How bout giving us a hint so we know what we're commenting on? Speed 400 parkflyers?
Sure doesn't sound like a Tigermoth or Litestik. They definitely land better with power on. BC |
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If it's a higher performance airplane with large control surfaces, a little prop blast over the tail can go a long way! The controls can be many times more effective with throttle on than off. BC is right, though - we'd need to know what type/class of plane you're talking about
Martin |
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Hi Dreamer and Basketcase, sorry for the delay in reply - good weather and I'm on holiday and just discovered GWS geared 370 and 300....wowowowow
Planes I've noticed this effect on are - Dirtcheap Parkflyer - Foam SkyRider with speed 400, folding 6x3 , 7x900NiMH Polyhedral, 10mm polystrene sheet, 1400cmx 30cm,full camber, geared 280 with12x8 or speed 400, folding 6x3 several wings on carbon 'stik' with either geared 280 or IPS A and 1047, including SE5a Biplane !! The effect isn't always there but happens enough to be suprising. It suggests that my planes will fly better when I understand the trim changes making it happen. Maybe I'm getting better at trimming the planes in flight or maybe I'm imagining it or is it ground effect at 4 - 6ft? I just discovered the benefits of motor downthrust so will be changing some of my motor mounts and see what happens. Thanks Flyfan More experiments to follow |
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sounds like
torque effect to me
when the motor is off the plane becomes a pure glider and stabilizes...also what dreamer said about prop wash on the surfaces....that will always effect characteristics (and is one of the biggest variables for aircraft designers since ww11 - thats what makes rear engine mounted jets desirable in smaller versions like the lear's) at higher alt there may be a current of wind, that is not noticed at lower level......the park flyers Jet stream....lol just a theory Belgy |
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Flyfan, I have seen the same thing on many planes that did turn out to be a lack of down thrust (in my uneducated opinion, anyhow). I didn't have enough and the plane was trying to nose up and I was countering with elev making the thing really mushy. It was especially noticeable on my flying wings because I would throw them off power and they would glide out great, but when I kicked the motor on I had to start working to make it fly good.
As soon as I get the thrust line in the right area, performance picks up on a mushy plane. On my ugly the motor is in line with the elevator, but the wing is up 4 deg at the leading edge which also was a trial and error find. So, it seems like down thrust or positive incidence can be the trick. On a side note, I had been running my ugly with geared motors and 8+" props and I had found that I needed rudder to counter the P factor (prop torqe?) because I didn't build in right thrust. I decided to try a DD280 with 4" prop for kicks. I fired it up, threw it out and it went waaaay right! With that motor I needed no right thrust or left rudder to go straight. Have fun! |
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Hi Flyfan, you've got the right idea by experimenting with it. Most of my experimenting was done with a CrazyMax, it suffered so may crashes that the down and right thrust changed constantly. I eventually used rubberbands to mount it that allowed easily shimming the firewall for experimenting.
What happens when you dead stick it all the way down from normal altitude? Can you tell where the effect starts? Is it repeatable? Can you power up, climb above it and do it again? If I remember right, from a thread here somewhere, you can test if the thrust is correct by trimming the plane for straight and level at normal cruising speed. Then shutting off the motor and diving just enough to get back to the same speed, if it still goes straight the thrust is okay. BC |
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Another possibility, a slow spinning prop say at low throttle will act as a spoiler and the plane will descend far more quickly than a stopped prop.
I use this method to land in my constricted flying area. For instance, if my plane is coming up slightly short of the runway and I want to extend the glide I brake the prop and the plane glides further than if the prop were freewheeling. If I want to drop altitude quickly I just give 1 or 2 notches of throttle and the plane drops like a rock with the slow spinning prop acting like an airbrake. Does this sound like your experience? Edit - the effect is more noticable with a larger prop. |
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Last edited by Vonbaron; Sep 28, 2002 at 06:00 PM.
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Thanks for all replies. I'm going to try some experiments this afternoon if it's not too windy.
I have avoided downthrust because I coudn't see what was wrong with the plane climbing on full power. I finally saw the light on Friday, indoors when a huge Kolibri style wing ( but 1 metre wide) was uncontrollable without enormous downthrust. My Skyglider is a dangerous beast and I now see the same effects as with the big wing so will be adding downthrust for todays flights. The trim checking procedure is a good idea, will do that also. Flyfan |
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Is it only a factor on non-symetrical wings? Maybe the more lift there is, from flatbottom to undercamber, the more downthrust is needed?
I always thought the Soarstar was supposed to glide well and even thremal with the power off. Something doesn't sound right. |
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Last edited by Basketcase; Sep 29, 2002 at 06:49 AM.
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