Shaunie Posted November 27, 2014 Share Posted November 27, 2014 Just nodded my Wottie for night flying.I'm generally pleased with it but...now when I slow it up it drops the right wing, aileron obviously doesn't help but a large chunk of rudder does. The LED strips are pretty close to flush but not absolutely so. Could these be the cause Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 27, 2014 Author Share Posted November 27, 2014 Sorry my stupid tablet goes all to pot when I add a picture to a posting. This is the LED strip.Shaunie. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 28, 2014 Share Posted November 28, 2014 Wow Shaunie - you have a turbulator! That will trip the laminar boundary layer off the wing surface and make the flow behind it turbulent. They are used on full-size aircraft (particularly gliders) to actually deliberately do that as there are drag advantages - check them out on the internet. But it doesn't apply to models! The reason is that on a full size wing the flow is going to transition to turbulent at some point anyway (as the critical Reynolds number is exceeded - that will happen around halfway across the wing usually) and there can be advantages in making it happen earlier or in a controlled fashion. But models hardly ever get a transition to turbulent flow - their wings aren't wide enough and they don't go fast enough. So they are not designed to have turbulent layers over their wings. Also a turbulator is a pretty precission bit of kit if it is to work predictably. I suspect yours is a bit "hit and miss" regarding when, where and if it is tripping the laminar boundary layer. You are going to have to get that below wing level I'm afraid! BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 28, 2014 Share Posted November 28, 2014 Oh - I've just noticed - its on the underside of the wing! Turbulators are usually fitted on the upper surface. Boy that will have a weird effect! No wonder its droping a wing! If you trip the the under wing flow that early you will have very much reduced lift! BEB Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted November 28, 2014 Share Posted November 28, 2014 If one wing is consistently dropping I would be looking to see if one strip was prouder than the other as that will cause bigger disruption to the air flow and reduce lift more on that side that the other I was just looking it up in Model Aircraft Aerodynamics by Martin Symonds but it got far too complicated for me!!!! Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 Hi BEB and Dave, That's what I was thinking,. I was aware of turbulators but thought that:- A. it was shallow enough not to matter and B. with the pressure on the lower surface being higher would it trip anyway? Obviously wrong on both counts. What level of surface smoothness do I need to maintain? I would estimate the level of protrusion to be about 0.5mm and it is about 1/3 Chord (where the spar is basically). I haven't glued the strip in it is just held with tape so I can lift the strip out with care and deepen the groove slightly. I have that book, time to do some reading methinks. Looks good in the air though! Shaunie Edited By Shaunie on 28/11/2014 12:40:52 Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted November 28, 2014 Share Posted November 28, 2014 0.5mm compared to a what? 30mm wing section? Still an appreciable %age alteration to the section Plus its going to cause some form of separation bubble on the lower surface disrupting the lift to some extent and as the effect seems to happen at low speed, is it stalling one wing before the other? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 28, 2014 Share Posted November 28, 2014 The weird thing about turbulators is that they need to be a very small step to work! They work by stripping the laminar boundary layer - which is only very thin - without disturbing the bulk flow - otherwise you don't just trip the boundary layer you make a "bubble" (as Dave says above). Even on the full size they are sometimes as small as 1-2mm above the wing surface! Really the only advice I can give is that to be sure of them not separating the flow you need them to be flush with the wing surface - or even slightly sunken if it doesn't interfere with their use as lights. BEB Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 Yes Dave, always seems to be the right wing! I'll take the strip out and reseat it tonight. The right wing strip is protruding at the outboard end, so I suspect that's the bit I need to sort out. Difficult to measure but the protrusion seems to be about 0.3mm. Will the thickness of tape still upset the airflow or will it tolerate that? Is sub-flush better than protruding? Flies fine with a bit of speed on. Initially I thought it may have been something else as the plane recently had a high velocity arrival that took some repair work and the initial flights with lights had the C o fG 10mm rearwards due to the weight of the LEDs in the tail. The C of G is now in the specified position by the way. I just thought it worthwhile to make my first attempts with a well flown plane that I was not to precious about and that was benign to fly. Seems it was the right idea, something lively may well have been unflyable. Shaunie. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 28, 2014 Share Posted November 28, 2014 Flush is best if you can manage it. No the thickness of the tape shouldn't be a big problem - well assuming its tape of sort of "average" thickness! BEB Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 It's only an "average" tape . Due to the type of foam the hot wire cutter left a fairly rough finish so I'll wrap some wet and dry round a dowel or something and give the groove a clean up. Shaunie. Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 Update, the strips are now flush, it still drops the right wing but only if slowed right up. It's not as hard to fly at night as I thought. Orientation is not as hard as I expected. The total LED count is 30 in each wing with 3 LEDs in each tip as nav lights, 36 down the fus and 12 in each tail plane half, no need for anything on the fin as it shows up well in the light from the tail plane, for a total of 126 LEDs. The total load is 750mA. Which equates to less than 6% of the battery in a 10 minute flight. Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 Double post for some reason. Edited By Shaunie on 28/11/2014 21:36:08 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 28, 2014 Share Posted November 28, 2014 Well done mate! The remaining wing drop may be caused by the lighting introducing a slight wing imbalance - right wing just a tad heavier. Might be worth just checking the lateral balance to see if you can sort it. Having said that most models tend to go one way or the other and if it not too big an issue - only part of the stall - you might want to just leave it! BEB Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 28, 2014 Author Share Posted November 28, 2014 Thanks BEB, as mentioned the plane suffered a fast arrival some weeks ago to the point I had to straighten the fuselage with hot water so it may not be just the lighting that is causing the problems. I wouldn't have been brave enough to modify a brand new plane so this is proving to be a very useful "toe in the water". Next thing is brighter LEDs in the right wing as green LEDs are not as efficient as red ones. The airframe responds well to lighting and looks near normal close in. Shaunie. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted November 28, 2014 Share Posted November 28, 2014 Cool...... Quote Link to comment Share on other sites More sharing options...
Chris Barlow Posted November 28, 2014 Share Posted November 28, 2014 I have the strips on my Magic and despite initial concerns about the airflow over the wing it pretty much flies the same as before they were fitted. From this To this, all fitted on top of the covering (Not a very good picture I'm afraid) A much deeper wing chord though and balanced laterally. Quote Link to comment Share on other sites More sharing options...
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