erkki67
Well-Known Member
What shape does it have?
What shape does it have?
Xfoil doesn't do square trailing edges (the spline can't have any sharp angles) so the trailing edge is either closed or open. An open TE simulates a square TE just fine for panel codes because they're not actually modeling fluid dynamics, they're just calculating the pressure and estimating the friction on each panel. If you can close that gap with a line segment your CFD might work with it. My guess is that as long as the finite TE thickness is less than 2 percent of the chord it won't make much difference for a 12% thick airfoil. For very thick airfoils a truncated TE actually produces less drag than a sharp TE. In any event it's just not practical or safe for airplanes to have knife sharp trailing edges.I had to close the TE in as the CFD does not like the open rear(Its attached)
I belive that's the center of pressure. Each panel has a vector representing the normal pressure on that panel. If you take the sum of the vertical component of all of those vectors (both up and down) you get the center of pressure. On zero pitching moment airfoils eg NACA 5 digit, some reflexed, and symmetrical this is a stationary point withing the linear range as displayed in the Cm graph. With normaly cambered and aft loaded airfoils it moves aft of the trailing edge at some low AoA which is obviously impossible see attachment.Does anyone know what the vertical arrow in the XFLR5 Pressure screen op point is supposed to indicate?
Yes a lot of the older airfoils are not to bad!The Arup S2 used the NACA M6 airfoil.
Xfoil doesn't do square trailing edges (the spline can't have any sharp angles) so the trailing edge is either closed or open. An open TE simulates a square TE just fine for panel codes because they're not actually modeling fluid dynamics, they're just calculating the pressure and estimating the friction on each panel. If you can close that gap with a line segment your CFD might work with it. My guess is that as long as the finite TE thickness is less than 2 percent of the chord it won't make much difference for a 12% thick airfoil. For very thick airfoils a truncated TE actually produces less drag than a sharp TE. In any event it's just not practical or safe for airplanes to have knife sharp trailing edges.
I belive that's the center of pressure. Each panel has a vector representing the normal pressure on that panel. If you take the sum of the vertical component of all of those vectors (both up and down) you get the center of pressure. On zero pitching moment airfoils eg NACA 5 digit, some reflexed, and symmetrical this is a stationary point withing the linear range as displayed in the Cm graph. With normaly cambered and aft loaded airfoils it moves aft of the trailing edge at some low AoA which is obviously impossible see attachment.
Thanks SlowFlight, I will include the profiles in the PDF's where I can.Thank you for posting. While I'm not sure I'll be looking for a flying wing unless it can be safely STOL, I'm interested in less Cm, and the wing shapes.
Hi NormanHere are a few positive Cm0 airfoil sections that I've found over the years. People have been trying to find the original ordinates of the Go 765 used on the Me 163 for years and the just don't appear to have been published so there have been a few attempts to lift them from a museum specimen. Unfortunately it's nearly impossible to get accurate measurements by hand even from a shiny new wing much less a beat up old war horse. This file "Gottingen 765 spline" is probably as close as you can get to the original Gottingen shape unless some secret WWII German tech report shows up. Next is a cleaned up version of the NACA M6. Not much improvement, just a little less drag at a couple spots on the drag polar and the L/D curve is a little wider but still that funny double hump shape. Third is a something I developed from an airfoil I found years ago. Don't know where the M35a came from or how I modified it it's been so long.
BTW The x axis on the drag polar in the PDF is Cd X 1000 to spread the curves apart
No I cant have posted it, I only have it in 499 points version, it may have been included in tests I showed on that original thread before this one.The M-35A is from the Marske Pioneer 3, I have it, I think I included that in those earlier tests I put up!?
I had indeed posted it with all those other Marske and similar ones..before going down to 299 points.No I cant have posted it, I only have it in 499 points version, it may have been included in tests I showed on that original thread before this one.
Ill convert it to 299 and put it here shortly.