Marc Freullet Posted September 25, 2012 Share Posted September 25, 2012 Hi all you Aerodynamicists. Just built this, Its my own design & scratch built. A few of my own theories have gone into the design. but it has not test flown yet &would like to know what your thoughts are on what flying charictoristics it may posess & any thoughts on set up etc the wing section is nothing spacific, but is semi or very nearly symetrical. Quote Link to comment Share on other sites More sharing options...
Lindsay Todd Posted September 25, 2012 Share Posted September 25, 2012 Looks very nice, I would go with some reflex on the ailerons (crank them up a couple of mm both sides) this should prevent any nasty tip stalls, also keep the speed up or the tail might start to loose some authority especially at high angles of attack such as landing approach or for that matter on launch. I would not expect it to be to temperamental to an exact CG but 30-35% mean chord should be fine. look forward to seeing others views and that all important first flight report. Linds Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted September 25, 2012 Share Posted September 25, 2012 Hi Marc, nice model. Have you incorporated any reflex into the wing? If not you are probably going to need some "up" trim to fly it. The wing will produce a net "nose down" moment, normally of course a tailplane rigged slightly negative relative to the main wing provides the balancing coulple. Without the tailplane you need some other source for this force. It can be delivered via reflex (a sort of turning up of the wing profile near the trailing edge) or if not built in then effectively trimming the elevons slightly upward will achieve the same effect. BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted September 25, 2012 Share Posted September 25, 2012 You beat me to it Linds! BEB Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted September 25, 2012 Share Posted September 25, 2012 looks good marc....everything fly's once .....the c of g will be the thing that will determine how it go's...and some reflex ....... do your first go's over some long grass..... ken anderson..... ne..1 ....long grass dept..... Quote Link to comment Share on other sites More sharing options...
Marc Freullet Posted September 25, 2012 Author Share Posted September 25, 2012 Hi & thanks I havent built in any reflex into the wings & at the moment the elevons are rigged neutral so on your advice I will give them a couple of degrees nose up trim even if this is not required its probably best to have it pitch up rather than down on the test launch I guess & trim it from there. I deliberated on weather or not to incorperate a rudder, I know that Delta wing shapes such as this suffer from adverse yaw unless differential aileron is applied ie more up than down, so Im hoping that the rudder will help here in the turn ie counteract the adverse yaw. What are your thoughts on this? Again the elevons are rigged at the moment for equal throw on aileron input. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted September 25, 2012 Share Posted September 25, 2012 Yeap - with ailerons that big you will almost certainly see some adverse yaw. But I wouldn't worry about too much at the moment as you have your rudder to help you point the nose in if needed. I'd be wary of mixing rudder with the ailerons in the Tx until you've had a feel of how she flies. This set-up can show strong tendancies to "tuck in" in the turns so you might find one trait (adverse yaw) neutralises the other (tuck in)! If you have the mix "hard wired" in, and she does show a tendancy to tuck the nose in when you turn, then you'll have a right "tiger by the tail" because everytime you try to turn the nose will go down and the rudder will just make it worse! In such circumstances you might in extremis even need opposite rudder - let's hope not! So I think the best plan would be to leave yourself the option by putting the rudder in manually - certainly for the early flights. BEB Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted September 25, 2012 Share Posted September 25, 2012 Marc, Strictly, that is not a Delta!! IMO (and from flying maybe 35 plus very similar tailless plank or swept wing plank models, many own design), adverse yaw, a tendency to tuck in, and needing to put the things into high angles of attack for landing (or launch) are simply not features of anything I have made, and I make no claims about my building or designing abilities. I use an online calculator for CG start position, and set the elevon null position with the lower surface in line with the rear wing section, which gives minimal reflex. I use excess throws and a lot of expo for a maiden. Tailplane less Planks, especially ones without a fan to give low speed air thrust over the surfaces, are usually fairly insensitive to "aileron", even ones your size right along the wing, and very sensitive to "elevator", so take that into account. I always part discus launch across the body with the left hand on the port wing, which with mode 2 allows my thumb on the Tx stick with Tx in right hand to fly it away from any launch. On at least two of my similar designs the short coupled rudder only added drag, and simply was not needed, so was taken off after a few flights, to no ill effect or significant loss of control ability. You'll be fine!!! Quote Link to comment Share on other sites More sharing options...
Marc Freullet Posted September 25, 2012 Author Share Posted September 25, 2012 Posted by Biggles' Elder Brother - Moderator on 25/09/2012 14:40:18: I'd be wary of mixing rudder with the ailerons in the Tx until you've had a feel of how she flies. This set-up can show strong tendancies to "tuck in" in the turns I can see your point. i think that,when a turn is initiated with ailerons & rudder & with no adverse yaw, in the roll the rudder will tend to yaw the nose about the normal axis perpendicular to the longditudinal axis ie nose towards the ground "tuck in" in this instance I can see that a little adverse yaw can be benificial. Quote Link to comment Share on other sites More sharing options...
Andy Ennis Posted September 25, 2012 Share Posted September 25, 2012 Marc, many years ago I used to fly a SAS Cygnus (not one of the modern epp things, this was balsa & ply with veneered foam wings). It had a very similar planform to your model, although the fin didn't protrude past the trailing edge, and there was .20 2 stroke up the front as slope isn't my thing. The model was a great flyer, becoming quite popular in my club with many people flying them. There was a slope version, which I believe flew equally well. Reflex, as has been pointed out already, was absolutely essential. I am sure yours will fly great! Congratulations on designing and building such a pretty model. Good luck with the maiden, and let us know how you get on. Edited By Andy Ennis on 25/09/2012 15:25:28 Quote Link to comment Share on other sites More sharing options...
Marc Freullet Posted September 25, 2012 Author Share Posted September 25, 2012 Posted by Dave Bran on 25/09/2012 15:16:40: Marc, Strictly, that is not a Delta!! Yes your right. I didnt use the correct terminolagy I meant a sweapt back wing of course. thanks for the correction Quote Link to comment Share on other sites More sharing options...
PatMc Posted September 25, 2012 Share Posted September 25, 2012 Looks good & it should fly fine Marc. Since it's a slope soarer it should be easy to establish a workable cg by a few test glides in a moderate wind. Once that's done it's just a case of tweaking the control throws. I wouldn't start with differential but about 50% exponential is useful at this stage. Once it's flying satisfacorily then's the time to establish the best cg position to suit your style (dive test) & experiment with the range of control movement & differential. PS note my avatar. Quote Link to comment Share on other sites More sharing options...
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