I found some of my old data and diagrams concerning leading edges and flaps from several years ago, and they fit somewhat with the original question and the flap issue that came up. While I certainly agree with Mike and others who have pointed to changes in Reynolds Number with atmospheric conditions, the relevance of changing camber with flap deflection, second derivative items, etc. and long ago wrote a little on those myself, I have been more interested in simpler things. So here - again FWIW - are a few items I explored and found interesting for my own purposes. Unfortunately, some of my old scans were done at low resolution for SSW forum and aren’t as clear as I’d have liked. I hope the wing section comparisons are visible.
First, my answer to a question above: for me, "penetration" is just a measure of how far a wing or aircraft flies into suddenly increased headwind from gusts or entering the upwind part of a lap before regaining its normal air speed. The better the penetration, the less quickly a wing’s airspeed and groundspeed slows, when encountering a headwind. While a less “draggy” wing is less desirable when accelerating downward in a maneuver, it has its advantages elsewhere.
Of all NACA reports I’ve found, NACA TN 763 relates most closely to the “Stationary flaps” that interest me. Seeing it again, I see that I did not remember what they call a “Guinn” flap quite accurately, thinking it to have a more abrupt hinge line at neutral and to be flatter. So it is thin, but very tapered. Anyway, the first two pictures below, from TN 763, do concern wings for flapless planes. Figures 1 and 2 (first picture) show the wing sections compared in the report. They are not symmetrical, but rather the most common of the 5-digit sections that they liked at that time. Their aft camber lines were straight from the “high point” aft, giving them low c.p. movement. I think such sections were used on the “Corsair” and later the “Bonanza,” among others. Aspect ratios are 6.0 for both models at Re = 609,000 (we fly at about 400,000-500,000; you can calculate yours here:
https://www.omnicalculator.com/physics/reynolds-numberNACA compared 18% and 15% sections, because the actual percent thicknesses of the 23018 with the Guinn flap was close to 15% at14.4% of the total chord.
The second picture is figure 8 from TN 763. From it you see that the “Guinn” Flap gives more maximum lift when not deflected than the plain flap (yellow line). NACA preferred the plain flap, due to lower drag and higher L/D, considerations for cruise range and speed. Other graphs in TN 763 show Cl’s for all angles of attack for each flap deflection, where data can be compared for our maneuvering C
L's. ...and yes, I have always been aware that we try not to fly at high lift coefficients near the stall!
I played around in Profili 15 years ago to create a wing section to suit an original flapless plane. Like John Miller, I modified one from the NACA “laminar” series. Liking its leading edge, but wanting a “friendly” flapless version, I moved the “high point” of the 63a010 forward to .24C and doubled its thickness. I got a section I thought might have less drag than the NACA 0020 (as for other thicknesses). The next picture shows it compared to the NACA 0020 section, both stock and with its maximum thickness moved forward to the same point. The leading edge “radius”, if it has one (elliptical, since thickness has been multiplied over the entire chord), is smaller than the 0020’s, but the transition curve seemed nice. So, I thought this less blunt section might have better “penetration.”
I wanted to see how a flat stationary flap would affect it and drew a version of the modified 63a010 with such a flap of only 10% chord. It is shown in the next picture. Unlike NASA in TN 763, I was more interested in preserving the shape of my wing section. So rather than making it thicker still, so that with flap, it would still make a 20% section, I just added the flap, making the flapped version into an 18.8% section. Since NASA and X-Foil had shown thicker sections to have a greater maximum lift coefficient in this range, I thought that any improvement in XFoil would be on the conservative side. XFoil’s comparative results are shown in the next picture, where curves 2 and 3 are for the stationary-flapped versions, while 1 and 4 are the unflapped version (1) compared to the NACA 0020 (4).
The last picture is of the LA .25-powered plane I built incorporating this modified airfoil. It had a D-tube Morris “New Millenium” wing that preserved the leading-edge shape, with a straight spar through the 25%-chord points of all ribs. Wanting to try a higher aspect ratio, I tapered the wing more than usual to ease the effects of gusts. Its MAC is at 45.8% of the half span, somewhere between the more ideal elliptical-wing’s (42.4%) and usual tapered wings' (47% - 49%). It was intended to get the stationary flap, after I’d flown it without, but unfortunately, falling victim to its pilot, it never got to the flapped stage. However, it flew well, even in moderate gusts, and it glided really well.
Addendum - just noticed this (new last pictures), a 23% wing section that is elliptical to 30% of the chord and then tapers along a NACA profile to 3.18% thickness to allow for a flap. Obviously, I hadn't used Excel for this one! Anyway, the profili comparison shows this fat section to be a bit less blunt than the corresponding 00xx section.
Topic: Blunt leading edge (Read 8243 times)