Cyclicscooby Posted July 12, 2012 Share Posted July 12, 2012 Hi Guys.. Here's one for the Aero boffins amongst you... It's may be something you're aware of, but probably not seen, especially with IC... I caught it on the glide back to earth at the end of a late evening flight.. Firstly, if you are a boffin, but have no Brushless experience, you need to be aware that a BL motor's magnets are strong enuf to cause a similar feel to 'compression' when turned by hand, past each magnet, so it's like a radial, with multi compressions per revolution.. (Soz if thats sucking eggs, but some might not know, and it might be important regarding the drag induced to overcome this.. ) So, the motor is cut, and were gliding back down 'deadstick'. When the airspeed is high enuf to overcome the 'compression', the prop starts to rotate.. As I turn, aileron ONLY, no rudder involvment at all, the plane appears to 'lurch' in time with the prop as it appears infront of the camera, in it's lower arc.. I think, when turning left, the prop helps it turn, but when banking right, it appears to inhibit the turn.. ?!?!? My little brain is suggesting this idea... As the 'near static' prop is diagonal, it will be interupting the airflow UNDER one wing and OVER the opposite wing, causing each wing to have different lift, then, at it passes vertical, the effect is switched, causing a left-right wing wobble.. This is enhanced by the ailerons coming into play and increasing the drag still further... Sounds plausable to me... OR... Is this the 'normal' effect of a prop, but at a lower / longer frequency... Slow-Mo if you will... Really curious to find out what people who know, think...!? Luv Chrisie.. xx PS - This is the first vid with my new 'took forever' splash screen, any comments of that would also be nice... Quote Link to comment Share on other sites More sharing options...
Garbo Posted July 12, 2012 Share Posted July 12, 2012 I have no idea but do feel a little air-sick Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 12, 2012 Share Posted July 12, 2012 Hi What an interesting effect! Is the ESC brake on? I would suggest your diagnosis is correct. The wobble is obviously in time with the prop presumably causing an asymmetric airflow over the wing. If the brake 'on' the airflow required to turn the prop is higher and so will be the disturbance caused by the prop. Your prop always seemed to stop in the same position suggesting the airflow is restricted in that region for some reason. This might make the disturbance caused by the prop even more noticeable. Quote Link to comment Share on other sites More sharing options...
John Olsen 1 Posted July 13, 2012 Share Posted July 13, 2012 I think there is a clue in what Simon says about it tending to stop in one position. If there is one point where the cogging effect of the magnets and poles tends to stop it, then when it is turning and passes that point it will feed a bit of torque into the airframe. If it was turning freely with no magnets and friction free bearings then it would not feed any loads into the airframe and would disturb the air very little. If it was fixed in place in any position then it would apply a fixed torque to the airframe, which would I expect be small enough to easily pass unnoticed. But if it applies a pulse of torque then the airframe is going to twitch a little each time it does. regards John Quote Link to comment Share on other sites More sharing options...
Cyclicscooby Posted July 13, 2012 Author Share Posted July 13, 2012 I'd noticed, but not noticed the prop stopping at the same position... If you know what I mean.. !! Makes sense that one point of 'extra' torque would cause that... Thats why I mentioned the magnets before, as I could appreciate their load implications, but not the effect.. So it could be a stronger magnet, or a slight bend in the shaft.. Very slight, cuz it appears fine, and there's no vibration, visually or on camera... This is my most over powered plane (130w on 450g) so kinda makes sense.. The Extra spins the prop too, but it just 'spins'.. I guess the plane weights more than the force from the Park480 It''s a unique phenomenon then..!? Never seen before..?? Do I win a prize..? Will there be a NEW aerodynamic effect, called 'Cyclicscooby-syndrome'.. I've definately got a syndrome.. !! LOL... Luv Chrisie.. xx Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted July 13, 2012 Share Posted July 13, 2012 Posted by Cyclicscooby on 13/07/2012 13:42:29: Do I win a prize..? Will there be a NEW aerodynamic effect, called 'Cyclicscooby-syndrome'.. I've definately got a syndrome.. !! LOL... Luv Chrisie.. xx Is that the aerodynamic equivalent of 'throwing a wobbler'? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 13, 2012 Share Posted July 13, 2012 Chrissie I dont think it is motor directly (I am sure you would be able to feel if it was significant enough to make the plane wobble) but I suggest it is airflow over the prop as it travels in front of the wing deflecting the flow 'up' on one side and 'down' on the other so creating a short lived aerodynamic 'pulse' every 180 degrees. For the rest of the rotation the torque effect would be constant. Well thats my theory! Edited By Simon Chaddock on 13/07/2012 21:13:44 Quote Link to comment Share on other sites More sharing options...
Cyclicscooby Posted July 14, 2012 Author Share Posted July 14, 2012 Interesting... ! Luv Chrisie.. xx Quote Link to comment Share on other sites More sharing options...
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