But hasn’t that has always been the case after WW1. Even I thought about it when I designed my quarter midget, FAI F3d and F1 racers, and I’m not an aerodynamicist.
This statement leads me to think that other designers are following the Redshift‘s wing shape that you introduced. Not that designers are now finally thinking of the lift distribution along the wing. Sorry, if I misinterpreted your statement.
Now with the manufacturing ability imparted by the molded wing I too am surprised it has taken this long for wings to look more like a high aspect ratio Spitfire with rear sweep (elongated ellipse). So many wings look to have a straight taper section and then the curve (ellipse) added at the tip. The Redshift wings look to have the progressive curve of the ellipse on both the leading and trailing edges starting at the root and ending near the tip. With the Pitbull 2 I still see the rather straight taper for a lot of the span.
Wing planform/Lift distrubution:
Pretty much correct Konrad. The ideal lift shape - if we can call it that - is elliptical, so an ellipse is what we need. Um...Except...a lot of the time on a narrow chord glider, the MAC and the CG can be too close together, which can lead to some particularly nasty unplanned departures from stable flight.
So what do we do? The best we can: which, as you note, is to reverse the ellipse so as to separate the MAC and CG a little more and so lessen the chances of stall prone instability - especially in turns.
OK, done deal, right?
Nope...there are other problems with a classical elliptical planform - even a reversed one - and they are the curved tips.
As we know, air will always take the path of least resistance, but if you look at the shape of an elliptical wingtip, then visualize some spanwise flow influence, add a bit of highly variable airspeed, then even in your mind's eye you will start to see a bit of a mess.
Those pesky isobars need to leave the wingtips (sources of many many stall behaviours) as smoothly as possible and with a controllable vortex (if possible) at the normal mid and upper-speed ranges. So we'd like the air at that point to do what WE want it to do and not what IT wants to do.
If you look at a real reversed intrinsic ellipse in a wind tunnel at glider aspect ratios (or UAV?) you will quickly find that the rounded tips are not only messy airflow-wise, they are pretty unpredictable too. The air can, and will, make sudden unpredictable departures in really odd directions. Not what we want.
Messing about with high altitude UAV's for a number of years, I have done a fair bit of wingtip testing and tried many wings tip shapes, and fins, and odd projections, and almost anything you can think of; and though it all the simple slightly angled clipped wing tip shines brightest. This shape gives the cleanest departures and the smallest vortexes at a wide variety of speeds - so that's what I use. If you get it right it will be pretty quiet (listen to a curved wingtip glider hiss and shriek) and may at times give a bit of a buzz - but only when going really fast.
I do try to prioritise my development directions and I think the wings are pretty much OK for the future. If you look at the Alpenbrise (which has the same type of wing planform) video's the wings work very well. For the smaller model V-Tail...I'm still learning - a lot. See below.
Revisiting the V-tail for a moment:
I do remember (in my admittedly rather obtuse thinking at the time) when I designed the Redshift that I was also a bit concerned with a skinny fuselage - and as you know the new one is even skinnier - with two large (V-tail) projections trailing in the wind at the back.
When we fly on the slope we are flying at a pretty complex vector if we want to fly straight and level. For example, if we are flying left to right, we have the wind coming at us, and also the lift generated by the slope itself which results in a pretty elaborate resultant. In fact, we are flying through a stream of air that is coming from below, front, right...hmm. So our plane is likely to be flying slightly nose down and nose yawed slightly to the right. To make matters even more complex there is a huge interaction between the speed of our model and the actual speed of the wind vector we are flying in.
So to test a sloping plane properly in a wind tunnel it would have to have the airflow vector direction correct (for any given speed)which normally would mean setting the test model at different vertical and yaw angles in the tunnel. If you can imagine that, then you can see why I giggle at computer simulations for slope planes. Anyway, the net result of that is that anything that is not symmetrical front and back that is flying in the convoluted wind/lift vector could be a bit of a liability, and can and will "weathercock" resulting in possibly quite large yaw and altitude change if the difference between the front and back area is too large - which we know it will be. Obviously if correct this is a good advantage and if not then the model is likely to wiggle around - even in level flight - like a racing snake with a chilli up its bum- help!
Basically, my (Possibly mistaken) idea again was to keep the projections as low as practically possible, while trying to weigh the overall benefits of the obtuse Vs Acute angle paradox.
Let's continue to share ideas and develop!
Cheers.
Doc.
